Since you're working on this, I'd say size less or equal to 10 makes bunker exploration enjoyable, but when they are bigger, for me it gets tedious, specially if I end up exploring the full bunker to find the exit. As for the inside of the bunker itself, now there are only corridors. Maybe you could add some rooms with special decoration: fountains (with water effect?), sacrifice tables, piles of gold ingots... Decorative elements that make exploring the bunkers have the "let's see what I find here" feeling. When I explore them now, my only objective is find a rare object to increase my rare inventory, and to find the second exit to get a +1 explored bunker. Also, on a side note, would adding animation to dinosaurs be very difficult? I don't mean walking, just moving their heads around so that they aren't inanimated any more. The same goes for trees, like leaves moving. Maybe creating 5-6 positions for each object would do the trick, or even less in the case of trees... Dunno, just dreaming from the ignorant side of development.