Lexicon of Dungeons is a 60 page pdf presenting detailed guidelines on building and constructing your own dungeon or underground fortress. The product is written from the perspective of a prospective dungeon builder (i.e. GM, although the content is equally player-centric), and provides all the monetary and asset-based tools required to construct that perfect dungeon. The product is written to be generic and systemless, and, as such, is suitable for any roleplaying game.
The product comes as a single pdf file. Background layout is decent, although there is an awful amount of empty space in the product. Writing and editing ranged from good to poor, and there are plenty of unnecessary typos, spelling errors and other mistakes in the product. I think the presentation could be greatly improved, both by improving editing and layout, but also perhaps by adding additional art to the product. For a 60 page pdf, one would normally expect to see a little more, though obviously not a requirement.
Lexicon of Dungeons provides everything and more information than is required to put together a dungeon. It covers all aspects of construction, from lighting in the dungeon, to hazards, to room sizes and corridor layouts, to defences, and decorations, locks and doors. It's quite a comprehensive guide to dungeon building and actually contains quite a lot of useful information that one would not normally consider. I think any GM that wants to use a dungeon as a backdrop for an adventure will be well served looking at some of the suggestions (mostly obvious but also mostly not considered, such as latrines) in this product. There's lots of useful advice on dealing with intruders, what not to do and what to do and consider, and what features and aspects can typically be found in the dungeon. It's quite detailed, though again the editing makes the organisation look a little hap hazardous and sometimes it feels like a section of the product just tails off without quite finishing.
Having read this product, I wasn't initially sure what to make of it. While there are plenty of guides and products that offer advice on building fortresses and/or dungeons, I've never come across one that actually costs this out, particularly for GM use. I guess if you're playing a party that builds fortresses and one player fancies a dungeon, this side of the product could be useful. Or, on the other hand, perhaps as GM you want to make sure that your rulers don't break the laws of economy. Either way, it was a rather unusual aspect of the product, though not detrimental. Aside from that, I think this product has some really useful content, even though it's presented in a rather unusual and sometimes humorous and flippant style.
As a guide to dungeon building I think this product is very useful, but as a personal preference I wish it hadn't been written as it was. As a more 'serious' product (not to say that it's entirely facetious) and with better organisation and editing this product could easily sit in any GMs library as something that provides tips and information on dungeon building. It's extremely useful in adding realistic touches to your dungeon and making the dungeon 'make sense'. Unfortunately, it's let down by some of the aspects I've already mentioned. Lexicon of dungeons is a decent product with lots of potential.