I made a little demo, but I'm having trouble with the upload.
In animated gif form:
Player (Maybe just a 32x32px red sprite with platform behaviour)
starts the game in a trap filled dungeon. Player death restarts the layout.
<img src="http://4.bp.blogspot.com/-VD_JBX9p_c0/UhpmXPdI4tI/AAAAAAAAAEo/RvJ2oByzLI8/s1600/w1.gif" border="0" />
Player eventually gets past all the traps/enemies/...? on the level, and goes through the exit:
<img src="http://2.bp.blogspot.com/-yaaBBRdmFDI/UhpmYBSsWsI/AAAAAAAAAEw/OOM8CCXFKEk/s1600/w3.gif" border="0" />
and is taken to the next part of 'Castle Dungeon' (or what-have-you).
If the player goes another way, it will refesh the browser with a different level made by a different one of us:
<img src="http://2.bp.blogspot.com/-16KFs92WvE0/UhpmX72n5ZI/AAAAAAAAAE0/D3kyQ2P2etI/s1600/w2.gif" border="0" />
Maybe we can make a really big and unpredictable game this way!
Anybody interested in helping to plan this out a little more?