This is the place to go whether you're a player that got a keep from the Deck of Many Things, or a DM that needs to make the ultimate dungeon experience. And don't be fooled by the title, this is also a quick way to see how much a character would need to start a tavern, brewery, or blacksmith shop. This book has four chapters, the first two about building your stronghold, the third about keeping it (or getting it), and the fourth with examples of what can be done with the rules.
Chapter 1: Building a Stronghold
This explain the factors that go into getting your stronghold starting, from picking your terrain, to choosing your walls, to labor costs. Simple and straightforward, it's enhanced by a "running commentary" in the sidebars that constructs a keep progressively as you move through the chapter.
Chapter 2: Stronghold Components
This gives you descriptions of all sorts of places and rooms you can have in your stronghold. But this is only the beginning. Everything from locks, windows, and doors are all addressed. What makes this book really interesting is how they describe the use of magic in the building, protection, and everyday use of your stronghold. In the previous chapter they mention that you can get discounts on your stronghold by casting spells (discounts on stone walls by casting wall of stone, cheaper upper levels by use of air walk or levitate). Special augmentation can make your walls particularly deadly by covering them with blades, fire, or frost.
Here is also the place where it explains the use of bag of devouring in your waste disposal, the need for everburning torches, and infinate uses for a decanter of endless water.
Another thing that tickled me was the mobility functions. Now you can have the floating wizard's tower you've always wanted, or the burrowing temple of the evil mole god, or castle that sinks beneath the waves (airtight and submersible).
Uses for several spells (some made permanent) are discussed, as are the uses of portals, and ever-popular traps. Things like having several magic mouth spells as a kind of tour guide of your home are rather amusing, but having that same magic mouth act as an alarm could be very useful.
There's a particularly fun section on wondrous architecture. There's rooms that reveal people's alignment, several different varieties that impede scrying, others that can be left as traps for the unwary, tables that reveal poison, or larders that are never empty.
In several places this chapter offers advice on how to place things in your stronghold (stables shouldn't be near the bedrooms, for example) which is a nice touch of realism.
Chapter 3: Strongholds in Your Campaign
This chapter discusses matters about getting your stronghold built. Everything from getting the locations, to hiring people to build it, to defending it. Most of it is general advice, but some of it a DM could use to add a touch of spice to what otherwise might be a routine endevor.
Also discusses is assaulting a stronghold. From the full-frontal assault, to the strike team, to the seige, this chapter touches base with all the major strategies. It doesn't go in depth, but it gives a place to start. Also presented are sapping rules, and collateral damage rules for walls.
Chapter 4: Example Strongholds
This is an example of what can be done with the rules. This presents five different stronghold, each examining different aspects of keeps. One is the "cheap keep", the uber-simple stronghold. One is an underwater stronghold, a huge dwarven redoubt, a floating castle, and a keep spread out over ten different planes.
Overall the rules are easy to understand and presented in a reasonable straightforward manner. However, some rules were slightly buried, so you must read the entire book very carefully as not to miss anything. A single window in each stronghold space is free, for example, but they don't tell you that until the windows section on page 42.
There were several minor editing gaffs, each enough to make me stop and re-read. There's a character that switches gender in mid-example, a sentence cut off in mid-though, an obviously single sentence made into three, a room with two names (in the Wondrous Architecture section, the piece titled the Cacophonous Chamber is referred to as the hall of noise in the description), and a mis-labled map. Probably there were more, but that's what I noticed.
Despite these minor flaws, I would recommend the book to any interested in adding some spice to any structure.