There are some major improvements you can add into your map.
First one being detail...
1) Right now the walls are very flat and it’s just 100% plain stone. What I would reccommend is putting in some wall details into the wall so then it isn’t just flat stone.
2) Add in a block palette so it isn’t just stone, perhaps add some logs or vines (for a ruin feel)
Another one is what many others have pointed out which is lighting... Well, if you put in detailed walls, what you can do is make the background of the details have glowstone or sea lanterns behind them. It lights up the area, but it also hides it.
And of course, you need to have a void underneath the last layer. Otherwise people would still be alive and the game would never end xD
Hopefully I gave you some tips on how to improve it and that you’ll take them into consideration!

Good luck with your map!
@ToxicFloof Opinions? xD