Here's a collection of posts by people on the theme of "Interesting Airfields and Flights", they're FSX but probably also apply to FS2004, and we can add more in this thread..

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7V1- Central Colorado Regional Airport in Buena Vista, Colorado. Just twenty miles north of 0V2, I have worked several times at this airport doing ARFF protection for several helicopter companies like QinetiQ, Agusta-Westland, Boeing and Agusta-Bell while they were doing high-altitude testing.
The EH-101 Merlin (RAF and RN versions), A109, AB-139, and AH-64 Apache have all been tested here.
The FSX version of 7V1 is better than the FS9 version because the roads around the airport are corrected, but still lacking correct location of buildings.
The nearby town of Buena Vista has never been included in any FS version.
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KLXV- Leadville, Colorado. The highest (9,927') airport in North America. It is also used for helicopter testing.
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SABA- Saba Island, Netherland Antillles. The strip is only 1300' long with a dropoff to water on both ends.
The default FSX scenery is okay, but there are several addon sceneries that are really good.
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YLHI- Lord Howe Island, Australia. Located midway between Australia and New Zealand, the default scenery is lacking, but addons are available for improvement.
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LHD- Lake Hood Seaplane Base, Anchorage, Alaska. If you like floatplanes, the busiest seaplane base in the world is located right next to PANC Anchorage International.
Watch out for the 747's taking off nearby when you are landing your Beaver!
At the real airport, cars can share the roads with airplanes. Airplanes have the right-of-way. I had to stop at a stop sign in my car to let an Otter taxi by.
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EKVG- Vagar, The Faroes Islands. Default scenery is okay but there is a great addon available.
Vagar is a great stopover for trans-Atlantic flights, but watch the fog!
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KPWT - Bremerton, WA
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Stevens Anchorage Int. (Sth central Alaska) (PANC) One of my favorite FSX flights is to grab my best bush plane and head North East up the Matanuaska River.
Just follow that as far as you want. Along the way you'll run into a bunch of little gravel and grass strips that you can do some touch and goes on.
The best two along that trip are Sheep Mountain (PASP) at 2270ft and at the end, Tazlina (Z14) at 900ft.
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0V2- Salida, Colorado. My home town airport. Unfortunately MS never updated it after the runway was extended ten years ago. 0V2 is surrounded by 12,000'-14,000' mountains.
The Collegiate Peaks mountains to the west are the highest range of mountains in the contiguous United States (Shameless tourism plug)
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Catalina Island (KAVX). It sits on top of a high peak with fairly steep drop offs on both ends. I have the FSGenisis mesh, so it might not look that way with default scenery.
They have an old DC3 that still delivers cargo there from Long Beach (KLGB) on a regular basis and if you try the same 30 mile trip in the default DC3 it can be challenging to get it stopped.
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Milford Sound NZMF. It's at the end of a fjord, surrounded by 8000ft cliffs. You need a special licence to fly there RW. Speaking of which, there are the French altiports  Courcheval, Mirabel etc.
There are some very challenging grass strips in Papua New Guinea (there's a very nice scenery series for PNG)
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EGNM - Leeds Bradford,England because it is the home airport of Jet2 and, as I'm a shareholder in their parent company, I like to see 'my' planes (courtesy of the World of AI).
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St. Barts is fairly challenging, also scenic.
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Go to Idaho, and try anywhere with 'Creek' in the name. Lots of quite challenging bush airfields, and many are strictly one way in and one way out...
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Have a look at the cool circuit in Idaho that srgalahad over at Sim Outhouse has set up for training for the RTW Race.
http://www.sim-outhouse.com/sohforum...ead.php?t=1281
This has become my test circuit for new GA planes, and I love to fly it ever again for the challenge.
The approaches to ID67 and ID41 in particular are just devilish.
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Denham EGLD and Fairoaks EGTF are quite interesting, because they are inside the Heathrow CTR (Class A), and require an SVFR clearance.
You can also transit from one to the other (Denham is North of LHR and Fairoaks is South) on an SVFR clearance not above 1500ft QNH, which takes you under the Heathrow approach.
Great fun to do on VATSIM, because it scares the bejesus out of the Heathrow controllers and big jet fliers!
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The Grand Forks approach can be very interesting in bad weather.
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Castlegar CYCG is an interesting one. Also there's one called S16 Copalis State Park that's right on the beach, but it would be more interesting if FSX modeled tides (the parking can be awash at high tide).
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Juneau, fly east to Snettisham 7AK2, climb to 5500 and descend through the mountains or fly west to Hoonah PAOH from there you can go to Skagway PAGY.
I also like Girdwood AQY to Whittier PAWR. Birchwood to Bold is nice.
Try Trail to Sullivan lake. These are all nice short flights, weather makes it way more fun.
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Trail, B.C. to O9S (Sullivan Lake)
Head up the valley towards O9S set your wind for either RWY 16 or 34 both are challenging approaches.
If you take the valley route following the river you can climb to 5,500'.
For 16 you can approach through the valley and get down to 500' AGL on right base to be at the right altitude for short final.
If you set up for 34 you can descend when you are over the strip and then do a tight descending 180 degree turn to final.
Or leave Trail and fly straight to Sullivan Lake climbing to 9000' to clear the peak, then throttle back (no problem on the turbo charged Twin Otter) and glide to the strip.
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Alaska:- AQY, Girdwood to PAWR Whittier
Take off from AQY and head up the sound to PAWR you can set up for either RWY 21 or 03 both are challenging.
If you are aiming for 03 you will not want to climb to more than 3500' slow down once you get over the small lake and then get ready for a quick descent on left base to short final.
If you don't plan your speed you will have to go around. For 21 try maintaining 3500' over the aerodrome and then cut the engines and try for an emergency landing.
Or leave AQY at dusk and find the strip with no RWY lights.
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PAJN, Juneau to 7AK2, Snettishan
Take off from Juneau and head east following the Gastineau Channel. Climb to 5,500' and take in the view for a few minutes before you have to start planning your descent.
If you are heading for RWY 33 I like to descend through the mountains just south of the strip, or you can follow the water right in and have a more leisurely descent. I have not tried to land on RWY 15.
This is another nice one to depart at dusk or add 7/8 stratus from 0' to 1000' descend to minimums (500') and try to find the strip. PAOH, Hoonah is another nice destination from Juneau, nothing particularly challenging about it though.
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Locarno, Switzerland to Lugano, Italy
Just a nice trip through the Alps. Some tight turns into Lugano if you aim for 01.
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VNRT, Rumjatar to VNLK, Lukla
I don't think I need to say anything about this one.
I only mention it for the few who don't already know about it. Leave VNRT and head north climbing to 11,000', default scenery didn't quite get VNLK right but may have made it more challenging because you have to do a tight left turn just before touching down.
Always fun, especially with gusting crosswinds
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CZNL > CBR2
Stay low, follow the river, and enjoy looking, then prep for a landing that is not easy, but not insane.
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London City- a single short runway in docklands with water and some tall buildings around it, try it in a strong crosswind
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I have been flying to unusual destinations and came across a challenging approach I thought I would share. Fly to the airport in the capital of the Comoros Islands, Moroni.
The airport is Prince Said Ibrahim (FMCH). Land on runway 02, it has ILS.
The approach to the runway is on a downward slope from a large volcano on the island. You need to turn onto final pretty sharpish otherwise you will crash into the side of the volcano.
Crank up the autogen to max (don't worry - the scenary is not that amazing so won't kill your machine) and it becomes more hair-raising.
The terrain slope down to the airport means that the trees are very close to the airplane during the approach.
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Some of my favorite Alaska flights are Juneau to Sitka- Nome to Unalakleet and probably Juneau to Unalaska (Dutch Harbor)

You forgot madria or something like that. Half the runway is on stilts over cliffs on the coast