In the AD&D adventure A1: Slave Pits of the Undercity, there are two areas on the upper level that have no doors or openings providing ingress for the players. This is probably a good thing, as a wight and a pair of basilisks lair within, but I’ve been asked by a friend what they’re doing there are how the players are ever meant to find them.
Just a bit of history: Slave Pits of the Undercity was originally written to be the AD&D tournament adventure at GenCon XIII (1980), one of a series of linked scenarios for the convention which were republished as the Aerie of the Slave Lords series. As such, the tournament map consists of a passage around a deserted section of the slaver complex before reaching the main area the group explores. The actual content of the deserted section is irrelevant to the tournament adventure: it’s just a linear dungeon crawl full of tricks, traps and monsters to challenge the players. However, when the adventure was expanded into the published adventure, the map of that deserted section needed to be drawn and it had to be stocked with stuff.
So, David Cook put in a wight and some basilisks. And because even the slavers don’t want them wandering the compound, they repaired the walls around that section so that they couldn’t get out.
There is a clue that alerts the players to this. In area #2, the wall shows signs of new construction. Particularly curious adventurers may want to know what it’s hiding – is it a secret treasure? So, if it is knocked down, the group get access to the basilisk lair (and, later, the wight).
The other way the group can get access is by climbing the outer (south) wall of the compound). The areas where the wight and basilisk are held are open to the air – an interior courtyard. This is a more likely course if they don’t know about the secret door when the adventure is used in campaign mode.
Of course, the wandering monster tables include the basilisk and wight from these areas, so it appears that the efforts of the slavers were in vain – the monsters can still escape. How? Perhaps by climbing the walls!
I know that some DMs have had the monsters burst out of the non-so-well-repaired walls into the tournament area, and I leave it up to you to discover other ways to make these monsters torment your players. Because nothing in AD&D terrifies players quite so much as petrification and energy drain!