One cool idea would be once you defeat the boss, you can choose to keep going, 'just one more room' and the deeper you go, the harder it is to get out
In the begining that was the idea. But for few reasons, mostly scope of the game, I had to drop it. Instead I plan to add few bosses into the game. Every time you encounter a new one, you will have to return back to the surface. This way after few runs you will be capable to venture deeper and explore more