1) James C. Boney's wonderfully evocative concept for Advanced Adventures #6
2) Allan T. Grohe Jr's piece on one-way doors and variable stairs in Knockspell #1
3) Philotomy's article on the megadundeon as the mythic underworld
Having encountered these three in quick succession and coming to the realization that I have in my possession more published worlds for D&D than I will ever be able to use in my lifetime, I had a bit of a brainstorm that I'd like to share:
I came up with an interesting twist on the classic dungeon crawl. Take the classic B2 Keep on the Borderlands and re-imagine the Caves of Chaos as a portal to multiple worlds. To start off with, take three or four of your favorite exotic D&D settings that have been collecting dust, because you'll never get around to using them. Maztica, for example. For each setting, populate the Caves of Chaos with setting appropriate monsters.
The characters start off in your standard D&D world, such and the Known Realms. They go off to explore the standard version of the Caves of Chaos. Little do they know that the caverns simultaneously exist in parallel on several worlds. At regular intervals, these parallel versions of the caverns switch places and anyone who is inside the caverns is transported to a different world. Thus, as the party emerges from their first successful foray into the caverns, they find themselves in a completely different world. When they return to the caverns, in hopes of returning home, they might find the caverns occupied by a completely different set of creatures. This can be used for as many worlds as the players have patience for.
Thus, with very little effort, one might be able to actually get some use out of those settings which, while appealing enough to be on the bookshelf, never were going to be used for an extensive campaign. And that one map from B2 can be an unexpected surprise every time a party dares to venture in to try and go home.