Here's the first draft map of the starting campaign area in Iron Canyons - imagine a huge canyon like the grand canyon with high grassy plateau on either side and some lush bottomlands in the basin. Most of the time its 5-25 miles wide at the bottom, and then big cliffs and caprock up to the plateau which continues as far as the eye can see. Humans live up on the plateau most of the time. Dwarven soldiers and priests and Skaven farmers have been slowly settling some ruined elvish cities on the plateau and clashing with the humans because of it.
There's a point at which the canyon becomes a mere 2 miles wide, with cliffs of about 2000ft on either side. All throughout the basin are huge pillars and there is an archipelago of natural pillars in the narrow part. Once, long ago, a major elvish city and trade hub was built around a bridge that spanned the two sides, with routes through cavernous dungeons and winding ramps and palaces and temples of death. What remains are its ruins - still dungeons and undercities and elevators and ramps and laboratories and ritual rooms and bound demons in summoning circles and ossuaries and prisons and experiments gone wrong and grafting surgeries and slave pens and monasteries.
And now the Dwarves have a small fort and a couple of thousand soldiers and settlers living in the area, and they want to clear the passages and rebuild the bridges, but its going to be slow going and dangerous work. As the ruins get cleared to the point of safety, dwarves will want to inhabit them, and so besides the elvish artifacts there is money to be made in real estate if the undead left behind don't kill all the investors or the dungeon-clearers.
Right, so the map. numbers are elevations. So at the north end, you're at 2000ft above basin floor. The next place bridged to is 1500, so there's a 500ft drop there - there is an uncleared dungeon of elvish undercity and sewers under the ruins that leads out from a tunnel onto that bridge and over to the 1500ft pillar, then there's a long ramping bridge to the next pillar at 1700ft (and ruins on top of all the pillars and caverns and everything else I mentioned above _within_ the pillars potentially all the way down to the basin floor and below.
The 1700ft pillar again has ramps and passages spiralling down to ~1200ft where theres another tunnel leading out onto a bridge over to the 1200ft pillar, then across another bridge in derelict condition to another waiting tunnel to a big 1900ft pillar. Thats where the richest elves lived and where the tastiest looking ruins are, at least from what you can see over on the North Ridge. Then there used to be a big final bridge over to the South Ridge but that's gone.
(posh elvish ruins hanging off the 1900ft pillar)
The Dwarves have managed to discover a bunch of different entrances to the undercity within the North Ridge ruins and have even begun to inhabit them. They've also rigged a temporary elevator down the cliff face to the first bridge, but the tunnel back into the cliff is unexplored, as is anything deeper than the surface of the 1500ft pillar.
In the middle of the ruins and near several entrances to the North Ridge undercity is a large magical circle that the elves used probably for demon-summoning or planar travel back when elves knew how to do that kind of stuff. Now, suddenly, people and monsters from other planes are appearing in it. (FLAILSNAILS multi-campaign tie in)
That's the basics.