At one point during our travels, we found our very own Daern's Instant Fortress, which makes camping outside to rest for the night relatively safe, as we are ensconced within an Adamantine building protected by magically sealed doors. Only the Cleric, who found the command words and bonded with the item, can open or close the doors, so baddies can't get in while we doze peacefully. And, in general, this works very well.
Camping in the swamp, on a section of land that we had tested to have good foundations by having our Mage jump around on it for a bit, we slept in the fortress. We had posted watches throughout the night, just to be on the safe side, with the character on watch stalking around the inside of the fortress, checking if anything untowards was happening outside through the various arrow slits the fortress provides. On the watch of the Fighter some Harpies turn up and start singing. Our Fighter, taking over the mantle from the previous player who failed any saving throw that he possibly could, was instantly charmed by these vicious creatures and drawn to them. But, hey, the rest of us weren't too worried, realising that even though he couldn't wake us up in his charmed state to aid him neither could he get out of the fortress to be chewed to death, as only the Good Cleric can open the doors.
And that was when the DM asked us all to roll to see if we were woken up by the Harpies' singing. The Cleric boldly rolled first and, just as his die came up on a fantastic natural 20, we were told that we needed to roll 'low'. Arse. The Cleric was the only other character to be awoken, but he wasn't worried. With his huge Will Save he could surely resist the Harpies' lure. Needing 2 or above to make his saves he confidently rolled his die to make the saving throw. And got a 1. Dammit.
So not only were the only two party members who were awake both charmed by the Harpies' singing, but one of them was the only person who could open the door to the fortress. Which he did, and the two of them wandered outside. As luck would have it, and we needed some at that point, both the Fighter and the Cleric snapped out of their stupors when they started to wade in to the water, at which point they rushed back inside and got the door closed. One Harpy was foolish enough to fly in before the door was closed, but a few well-placed arrows persuaded her to leave us alone.
Still, Daern's Instant Fortress remains a good item to own. In principle.