For me, Tin Tower is still the best dungeon in Pokémon. Everything about it is perfect- the location, the music, the tileset. It just builds up the encounter with Ho-Oh so wonderfully, and the puzzle was unique for the time and I always found it relaxing to go through rather than infuriating like a lot of other dungeons puzzles, but it still provided the challenge you'd expect leading up to a Legendary Pokémon.
How a GameBoy Color game made by a few people in a couple of years managed to capture these ancient Japanese vibes so well is a mystery to me.
Honorable mention to HGSS for making the entire area and encounter absolutely beautiful too.
https://youtu.be/ZIG0-ogili8https://youtu.be/Kr5ux-hejyMhttps://youtu.be/coS_Uua9B-o 