This set of plans depicts a well-constructed subterranean fortress that guards a tunnel. It's a tough nut to crack, but the daring may be able to conquer it, despite it being a comprehensive establishment well-suited to its role and to long-term habitation by its Drow defenders... of course, even if it was built by Drow, you may decide that they have moved out and been replaced by other forces, or even opportunists! The introductory notes provide several ideas for adventures using the outpost, but there's plenty of scope for your own adventures...
The fortress has several levels, described as 0, 1, 2, and -1 (this last being in the shape of a spider and which would make a good temple to Lolth. Being subterranean, there is no 'ground level' as such, although for internal logic level 0 probably can be considered so - it is the first level presented and has a front door! And a back one, for that matter.
The first plan, Level 0, provides for an open approach guarded by two towers between which there is a solid wall, all well-furnished with arrow slits. Behind this imposing facade there is an open courtyard which, if this fortress were outside, would be open to the sky, Beyond this is another wall (and more arrow slits) while to either side there's a series of storage rooms, barracks and a mess hall. The kitchen appears to be in a corner of the mess hall. Can you but find the secret doors, there is a passageway from the open approach to the storerooms on one side, bypassing the defences. Otherwise the route through the fortress leads through a couple of halls, the second lined with pillars, to a set of double doors that open to the area beyond. This side does not have arrow-slits.
The second plan depicts Level 1. There are numerous smallish rooms, the continuation of the towers and a gallery over the open area in Level 0. Of note is a large pillared hall with the depiction of a spider on the floor. There are more passages to one side, accessed by a secret door but not apparently going anywhere (unless you decide different, of course).
Level 2, the next plan to be presented, is much smaller, being a series of chambers towards the rear of the fortress. It provides comfortable quarters for the commander, with space for entertaining, and a secret door to further passageways - perhaps a means of escape if things get too rough?
Next up, Level -1 is, as mentioned earlier, spider-shaped. There is a pillared hall in the centre, and each 'leg' of the spider ends in a small room. The introductory text suggests these may be cells for prisoners. The final plan is labelled 'Cross section' but is quite hard to interpret. It doesn't really add anything to understanding the fortress' layout and is rather disappointing.
There is limited customisation, and both blue and black versions of each level. There are also some pages for notes, but you have to print them out and scribble on them.
Overall it makes for quite a nice fortress, either underground as intended or even in a narrow valley or mountain pass aboveground if preferred.