It's a free download (HERE) that guides you through the life cycle of a dungeon with various ages and hordes of creatures moving through. Writing down the history and reviewing it can be quite fun.
Watching the following video made me want to have a try myself and may similarly infect you.
I just finished a quick attempt at this fun little pdf this very evening and thought I'd drop some pics. My own artistic skills are fairly lacking, so excuse the rough drawing, and similarly the pics might not be too hot (using my cel phone as the best digital cam I have). It's not totally obvious, but you layer up tracing paper after ages to start the next one and allow some changes to be made.
We start off in the primordial age. Various caverns form, as well as an underground river, emitting from the lake to the east of the moutains. A great wyrm (purple) finds a sleeping hole deep in the earth with its hoard of gold (yellow). A strange gateway is present in a perfectly spherical room which will bring a strange fate to those who finally discover it. Finally, a seem of gold cools into existance along a fault towards the deepest depths (red line)
Finally a new construction of housing breaks into the spherical room with the strange black gate. Before the workings are complete the gate flares open. No one knows what is discovered on the other side of the gate, nor if messengers came, but the dwarves gathered their belongings in a hurried, if organized manner, and disappeared through the gate and into mystery.
A great disaster befalls the area, and a volcanic eruption occurs in the western part of the mine. A lava chamber with a vent explode upward. The confluence of the underground river and the heat of the lava create a steady steam pillar that the locals eventually call 'The scald'.
Humans (orange) populate the area to the east of the mountains with a castle, and farms. Gnomes (blue) move into the spherical chamber, while earth devils populate the great hall. A massive elder Xorn (purple) moves into one of the Dwarven barracks, and 2 mimics and an anheg (pennies) populate other areas (the mimic with the dragon (button) obviously hiding *very well* amongst the hoard).
The earth devils expand into the wyrms rest chamber and level the floor and construct a small fort. Earthmen (red blood markers) arrive and exand through the lower dwarven workings. The other mimic is cleared out by the devils.
The humans are fruitful and multiply. The earth devils are beset by the gnomes and Xorn and are forced back by a series of bloody assaults into their recently constructed fort (now a dime). These constant attacks have stripped their wealth from them.
Tunnel Wyrds arrive in the great hall. The gnomes continue their relentless expansion in all directions (blue). The earth men face depredations of the gnomes and the Xorn.
The deprived and maddened prisoners of the oubliette move towards the scald, hunting for food and sport. The humans harvest the power of the windswept moutains as they build a large mill on the mount. The wyrds have driven the gnomes back from the grand boulevard but the gnomes continue their steady expansion in other areas. The remaining earth devils finally abandon their colony in the wyrm chamber for richer opportunity in other lands.
ADVENTURERS!! Moving down the underground river the adventurers wipe out the the wyrds in the grand boulevard and great hall. With their additional wealth they take the perfect xorn hole deeper into the chaotic earth men areas and manage to wipe them out as well. Their encounter with the gnomes (lawful) is more peaceful as the gnomes ask them (quest) to rid the depths of the horrible eldar Xorn. Alas for the adventurers a clever ambush slaughters the lot, leaving the Xorn with a legendary pile of treasure that many rumors spread about.
The lay of the land as the rumours of fantastic wealth usher us into the age of Villainy, and the arrival of......THE THOUGHTLORDS!!