For me a great sample of this is STONEMAZE by Pan-(G). This map, basically made for the DeFRaG mod, is a really huge maze with the walls a little higher than the player. Because it's a labyrinth with the walls slightly higher than the player, it reminds me of the map 03: 2 Useless Keys of the Doom II 15 speedmaps megawad The 12 Days of Doommas compiled by BluePineapple72. The map is done by DynamiteKaitorn, and despite the fact that it's a speedmap, I really like this one (as well as other maps in this wad). Just like I like STONEMAZE. And what I also find funny is the fact that both those maps were made as labyrinths, where Stonemaze would set a goal to test the player's speedrunning skills, while 2 Useless Keys would concentrate on being created fast itself. In my opinion, both maps' palettes are almost ideally suitable for Christmas.
In this case it's only 2 particular areas, but still, the cafeteria on CITY1 by KRAFTWERK2K1 seems somewhat similar to me in it's concept to MikeDonalds on the Doom 2 map Doom Center by Doorhenge. Both levels have a skeleton as the only employee, and both those skeletons are supposed to serve burgers 😅 It's probably just a coincidence, but still, I find very cool the fact that Classic Doom and Quake 3 mappers have spiritually similar ideas, it shows the unity in the way of thinking in our communities, even if it's unintentional.
If you can come up with some other examples like that, no matter if it's both Q3 maps or only one of them, please feel free to share it here ;)
Two more maps that obligatory come to mind are LDAQ3A05CTF by Lee David Ash and WVWQ3DM7 by @wviperw. On both of these maps, you go on an unforgettable journey through the green-foggy forest, but with a low probability of remembering many details :) I've seen @KommissarReb (SW12) also mentioning that it looks like Decidia in the LDAQ305CTF's comments section (lvlworld.com/comments/id:1442).
I have also noticed @Pasquake and @EmeraldTiger mentioning the resemblance of WVWQ3DM7 and Tokara Forest from Unreal Tournament 2003, later appeared in UT2004, in Decidia's comments section, which is something that I totally agree with (lvlworld.com/comments/id:1612).
Five more maps that all together come to my mind at the same time are COLDWARCTF by Sedric, KELLBLACK by @Kell, FROZENCOLORS by 79DieselRabbit, KINETERRA1 by Kit Carson & Nemo and KILLFACTOR by RUSKULL ]CWA[. I think this is simply because these are all CTF maps that have mountains with changeable landscape C:
Next, another very interesting map is MG_FINAL by @sock & @Mr. Lake. From level's readme file:
I took the original map and de-compiled it to get an idea of structural
scale and where all the items were placed. Once I had a compiled version
of the original map I stripped out all of the detail and converted
everything back into basic concrete blocks. I quickly tested the map
to see if all the original game play was still intact and luckily
everything worked fine.
Thus, this map is actually based off of Mr. Lake's EG_CTF1 and highly improved with significant gameplay changes. So the authors collaborated on this from some point of view remake, and therefore logically, it's not a coincidence that these two maps have the names which are so similar to each other: Evil Gemini CTF and Mystic Gemini. They are CTF Gemini ;) There's much and much more level's (re)building information provided in the readme concerning the map creation history, which I really find very interesting, so I definitely recommend take a look at this!
@Tig mentioned another CTF map that has its bases very close and visible to each other, which is
Q3RCTF by Ricochet. Personally, I have some memories about another level like this. It also has the bases located very close one to the other, and in this map's case, almost back to back, however the blue and the red zone are analogically separated with the glass. The only way to reach the enemy team's half of the territory is to go up through a very long tunnel or something. This map is relatively small and absolutely symmetric IIRC, but I cannot remember the name of it... If anyone has recognized the level that I'm talking about, I would be very glad and thankful to the one who'll reveal its name :)
Then, a quartet of maps which have quite a similar atmosphere / color gamma is GNC_ENGINE by GNC, CHARON3DM10 by Charon, BAL3DM3 by Bal and MADDDM1 by Maddman99. This is because they are made in the red color and some of them have the same textures, IMO.
Finally, two more levels with similar colors are COMPLEX by SMKnight and Star Trek - Doom Invasion by Thomas Spaulding & Grant Jacobs, which is a custom map for Doom. These ones are similar in the color palette that was applied to them: red, white and black. Furthermore, both of these two maps contain mazes in them and a reference in the title (GoldenEye and Star Trek).
EDIT May 29: Star Trek - Doom Invasion is a custom map for Doom 1, not for Doom 2.
Edited 93.07 days after the original posting.
Finally found this map (it appeared in recent downloads today)! It's AXZCTF2 from AXZCTFMAPS by Derkesthai (the one on the screenshot).
Edited 1.77 minutes after the original posting.
However, that doesn't stop each level from being unique: Shibam offers some air ducts close to those in the original Quake as a transport method, while Dawn of Time provides some really good opportunities for gameplay in CTF mod.
Actually, I knew a map called Iran from a game called Tanki Online. It certainly has some similarities with both of these levels.
Another map that I discovered just recently and which is similar to these ones is Q3NEM06 by @NemiX There is one even more such level to mention which is REDQ3DM4 by Redfella. All these maps are made in the industrial style, they have similar color palette, and all of them except BAL3DM3 use Vendetta textures by Rorschach.
Although it is featured on the site, so I should probably have discovered it earlier :D
Edited 1.12 days after the original posting.