From publisher blurb:
"On a lone outcropping of ancient basalt, a low, round structure overlooks the surrounding landscape. Built from the same indigenous rock, its walls are several feet thick with windows interspersed around its circumference. It appears to have two major sections, with the lower measuring eighty feet in diameter and the upper measuring fifty feet. The roof is flat with a high wall surrounding it, punctuated every few feet with small square opening, like an arrow slit. There are twenty flat, rectangular windows around the base and twelve circular windows around the upper section. The upper windows are about two feet in diameter, though little can be seen from the ground. Peering into the lower windows, one can see that they have been sealed by some sort of steel plate or shutter from the inside."
The purpose of these books is to help DMs put together an interesting encounter in a short time. Each Adventure Keys release does this by starting with a unique location that can be inserted seamlessly into an existing world with little or no modification. They are modular, with many options and variants available so that the DM can customize it to suit their needs.
There are six sections that include the Location, Hooks & Goals, Characters, Trappings, Threats, and Changes. All but the first have multiple options each, and since the DM isn’t limited to using only one option, the variations available are quite numerous. Sections can be used or ignored at the DM’s discretion, or even modified based on the situation or to scale its Challenge Rating.
The options are deliberately non-specific for ease of use. The DM can include them as they are, combine them, or use them for inspiration to create an entirely new options.