Well there are a few high quality maps for you... By Outdoor I think you mean "terrain", so my answer will be accordingly.
The UT99.org Community Mappack 2 has DM-UTR-Kamah (Creavion) in it.
There is DM-Marklar, very tight map.
And there is, of course, my DM-TMC-Narean. A study of winding walkways, caves and an ancient temple at night.
CTF-DisposableHeroes has always been a favorite of mine.
CTF-Shadar (ElChicoverde) is probably the most impressive outdoor CTF map. It's huge and plays quite well.
Both CTF-ProjectX and ProjectX2 are also recommended. Their terrain didn't really age well, but both maps are huge and well designed, especially PX2.
CTF-Wether (Bot40) and CTF-DeNovo (Ulukai) both feature a lot of open skies, but are both no-terrain maps.
CTF-UTR-Syntra is set in a small valley, looks quite nice.
Don't have a good selection of Domination maps, but DOM-FoT-Xenora of the FoT3 package features a good bit of terrain. It was done by Derdak2Rot and me.
Now there are a few interesing maps:
AS-ColdSteel, ColderSteel and Coldsteel2 are all gorgeos maps, huge and really well playing. I think you can get them in the packages AS-Coldsteel and Cold(er)steelpack...
There is AS-FoT-Chronoshift by our very own Revelation, featured in FoT5 (check FnBs page for that one). It does feature part terrain, part outdoor, part REALLY impressive tech facilities in one even more crazy AS map.
In the Forts of Time package, there is also AS-FoT-Shasmah, a nice Nali / Ancient themed Assault map by Derdak2rot (where is that guy? he made some awesome sauce back then)
And to respect the classics, also check AS-Bridge. Really old, really not aged well, but considered a classic back in the day.
€ As for getting all those maps:
I have mine in my signature as a neat get all in one package.
For the FoT mappacks, check FnBs homepage
For the other maps mentioned, you can check either mapraider or ut-files (see the link on ut99.orgs mainpage).