>>96367297 (OP)
>the hook
Why are is your party entering?
While "get paid to kill things" always works, it can help for your players to have a slightly more IC reason to enter, like to recover someone's family heirloom
>the challenge
Enemies filling it, traps inside
Generally you dont want each individual encounter to be a slog and you dont want to keep repeating encounters
Basically dont just have 3 rooms in a row filled with skellymen
Instakill traps that can only be found with a PER check are not exactly going to be fun for your players, so instead of saying "roll for perception, you fail, you get hit with a flame trap" describe the room as having black scorch marks and the smell of pitch in the air and see if they are on their toes
And let your party come up with alternatives, if they want to sneak instead of fight, that should be a possibility
>the gimmick
Doesnt have to be huge, but just change up their usual approach
Describe furious winds that make flying, climbing, and long range arrows useless
Or describe thick, acrid, smoke that requiees everyone to wear filtered cloth (cant cast spells that need magic words, cant drink potions, and cant communicate past X feet)
Maybe some developments can help instead of hinder the player, maybe there are open vats of liquid that can be toppled to slip baddies
>personalities
Dont just fill dungeons with enemies
Maybe have a a non-combatant who will ignore the players if they ignore him
Prisoners to talk to and free
Or arrogant enemies who feel the need to banter first