cmrscorpio said:
3) inside one of those ridiculously colossal++ epic monsters
I actually did that. The PC's were inside a stone colossus (a war machine from Xen'Drik), trying to stop agents of the Emerald Claw from using an artifact to transfer the mind of the main bad guy into the colossus, giving him a virtually invulnerable body of godlike power. Halfway through the fight, they succeeded, and the rest of the fight was trying to remove the artifact as the colossus rose and began to walk.
A ritual circle--all that is needed is a sacrifice within the circle, and something horrible will happen. If the PC's know about this in advance, it'll be fun as they try to avoid inflicting lethal damage against the much weaker cultists. Of course, the cultists are under no such restriction themselves....
In islands floating in an infinite void. Some kind of flight would be handy. As it happens,
I've already designed a map for just that.
In a museum. Innocent visitors have to get out, those antique weapon displays come in handy when you get disarmed, and it gets interesting when the necromancer the PC's are fighting animates the Megaraptor skeleton that formed the centerpiece of the main hall.
Any interior arena, on fire. Falling timbers, the exit is being cut off, the floor gives way at a very poor moment.
An area of scrubland, just after the monsoon starts. The rain is so intense that you can't seen ten feet ahead, it's hard to move as the ground turns to liquid mud, the noise makes it impossible to hear anything, and then the lightning strikes start....
A cramped and long-neglected graveyard. All those tombstones make it really hard to move about, sephulcures provide useful vantage points, and some of those ornamental statues might actually be construct guardians, programmed to react with deadly force if their tomb is damaged.