first of all i need to ask something, why in meowiarty's dungeon or big ben do you have the ability to go back a floor, but in Edrik's vault if you try to go back a floor you are outside? I Gavin Darkshard was on the last floor of edriks vault, but when i thought my game glitched, and i turned around to go see if i skipped anyone, i was put out onto the sidewalk right outside the dungeon , i tried to go back in hoping it would put me back on the final floor, but i was back on the first floor i was infuriated why is there such a diference between these two dungeons Kingsisle?
Only KI can answer why they did it this way (I am guessing because it is more challenging to not be able to leave to get more life) but many a wizard has made that mistake. Don't let it frustrate you too much. Just take it as a learning experience. I have screwed up many things in the game in my year of playing but I never made the same mistake twice!
Meowriarty's Tower is a physical tower with floors and stairs or an elevator. Some multi-level instances, especially in Dragonsypre, are really vaults that have multiple levels that are separated by magic portals. Once you go through the portal, you're teleported into a new level, but if you go back the other way, you're teleported outside.