CURIOSITY can be one of those things. "What new aspect of this story waits in the next level/room?"
The culprit is a scarred up female Hobgoblin named Ya'viis. Her horde has moved into a labyrinth that was buried by an earth titan
A helpful NPC is great for this aspect. A druid or ranger who has been keeping an eye on the goblins and hobgoblins' comings and goings. "They have slaves in there. Bought with gold by brigands in the first level."
3. Freedom (for the slaves)
and 4. Gold
You've got 2 enemies - the brigands and the goblins.
THAT'S IT. It can feel boring fighting goblins and hobgoblins and bugbears forever, but they, and humans, are INFINITELY CRAFTY
Immediate payoff - kill the bandits, save some slaves. Slaves know nothing, but a brigand may give details about WAY LATER.
The next room, they find the brigand's staging area, where they drag slaves for the hob goblins. Who's there? Ya'viin. She sees them, has "BONE CRUSHER," her ogre consort smash apart the exit and collapse it.
That DIRTY RAT!
The PCs aren't trapped, THE ENEMY IS.
Room 42 - they find a passage that leads to a vast array of stolen treasure.
Your players LIKE being familiar with their enemy, knowing how to best them.