Sweet thanks a bunch everyone. Okay a place like a dungeon seems easy enough to keep it interesting but what about a warehouse? Currently the pc's are on a Prove Your Worth quest for the Veiled alliance. They must poison 2 heavly guarded merchant house [FONT="]Txalaxa distillers. (yes house txalaxa can afford to have 1000 pound metal pots) which is why they are heavily guarded. But in a place such as this how could you make a simple warehouse seem interesting?[/FONT]
As Pbartender notes, you can still enliven even a warehouse with good description. I tend to prefer short and sweet descriptions that catch the attention - mentioning bats or birds fluttering overhead is a good touch, for example.
In terms of elements that might help increase tension, again, you can have them make minor discoveries that help build connections through the game world. As they sneak towards the distillery, they might come across some trade notes that reveal how House Txalaxa is cheating some powerful merchants. It has little impact right now, but after completing their quest, the PCs have to decide what to do with it - turn it over to the Veiled Alliance for some extra insurance against Txalaxa? Reveal the info to the merchants in order to get a reward? Try to blackmail Txalaxa with it? Or destroy it and hide any evidence of their presence at the distillery?
You don't want such side-quests to overwhelm the main mission of proving themselves to the Veiled Alliance, but it can help give them some other elements to think about along the way.
In terms of more immediate decisions to make that don't really involve an obstacle - maybe in one room, they find some dying slaves, overworked by Txalaxa. They can easily sneak past the slaves without notice, or they can spend time tending to them, but risking discovery. This scene would help emphasize the harsh nature of the setting, help stir up the PCs anger against Txalaxa, and present them with a dillema over how to proceed.
Or you can add in elements that could help make other parts of the mission easier. While sneaking through the barracks, if they spend time investigating, they uncover evidence that one of the guards is stealing from his bosses, or has some other secret. Later, they can use that evidence to convince the guard to leave his post rather than having to fight past him.
Anyway, no idea how appropriate these scenes would be for your adventure, and you don't want to go too overboard with secrets hidden in every single room - but those are the sorts of encounters that can present some memorable elements for PCs that don't involve a direct challenge or fight.