This adventure is located in Raging Swan's Lonely Coast campaign setting but, as it deals with remnants of a far-distant past just about everybody has forgotten about, it can be placed in a suitable location in your own campaign world with minimal effort. Before getting into the adventure, however, there is a very clear explanation of how encounters are set out showing you exactly where to find each item of information you might need whilst running it. A lot of people lay encounters out clearly, but actually explaining your methods in advance is a nice touch. Traps and monster stat blocks are similarly laid out in detail, and this is followed by an overview of the Lonely Coast, to enable you to establish the adventure's location easily, complete with a good map.
Next comes an Adventure Background and an Adventure Synopsis. The Background gives all the detail you need about the situation, and the Synopsis walks you through the intended sequence of events. There's a note about the best way to relocate the adventure if you don't want to use the Lonely Coast, and then more detail of the complex whose exploration forms the actual adventure, complete with a beautifully-detailed map that has a 'hand-drawn' feel. Several ideas are provided for why the characters come across this adventure, including blind chance (after all, it's over ten centuries old and most folks don't even know it's there!) as well as reasons for why they might be in the area about other concerns. Neat.
The adventure proper then begins, with everything you need to run the characters through finding the entrance... complete with pictures to show your players as well as detailed plans of each location. This is well-resourced indeed! Everything is very clear and detailed, you will not need to spend time rummaging through other books to find additional information.
The adventure itself is deliberately challenging for the intended Level 3 characters, partly because they have ample time to rest, regain spells, etc., as they explore and partly because, well, it's intended to be a dangerous place anyway. But the rewards are pretty good, especially for those who like - or know where they can sell - ancient artefacts and knowledge.
It is a well-devised and beautifully-presented dungeon crawl, with a coherent underlying rationale and plenty of exploration and combat to challenge the most determined adventurers. Moreover, it is not - as so many such adventures are - very linear, the characters have quite a lot of freedom in where they go and what they do whilst exploring the depths. There's an excellent atmosphere of treading ancient halls that have not been disturbed for countless generations... and even some follow-up activities if desired.
[5 of 5 Stars!]