I've got some ideas for quest #9 to continue the story, but I need to figure out the store triggers for new items. It'll likely require a code change.
Every level has a secret room that takes some doing to get into.
The first level's is the easiest to get into, but is made to be hard to find without a magic map.
The second level technically has 2 secret rooms. The first, which requires an epic fight, grants you access to the second unless you are a rogue who can simply jump to the second, with enough practice.
Level 3's secret is the hardest because you need flying to get to it. I put it in so that someone returning has more to explore, but I'm certain someone else will figure out a way in that I didn't think of. Like jumping on a monster's head or using the leap spell.
Level 4's secret rooms are just those locked doors, but they exist strategically because thieves can easily pick the lock, but other classes have to draw attention with spells and have enough mana just to get there. (not to mention, most classes don't have the runes for knock/force door yet) However, there are more items sitting around in plain sight in the outdoors section if you can get high enough to see them. Only the rogue jumps high enough at the start to get to these ones.