Following on from The Halls of the Gorgon, Hidden Halls is a mini solo that lets you delve into the secret second floor of Ogul-Duhr. You don't need to have played the previous solo to play this one. Hidden Halls is superior to Gorgon in many ways and stands out as a classic Tunnels & Trolls adventure.
Orcs have taken over Ogul-Duhr now the Gorgon has been slain. However you are told of great riches that can be found in the secret second level of the dungeon and set out to find it.
There's much more happening in Hidden Halls than Gorgon, from deadly traps, a giant golem, lots of passageways and truly tense moments. The 1d6 encounter table from the previous solo has been upgraded to 2d6 and features more humanoid monsters than before. There is also an arena where you fight some awesome foes, including a hydra that can permanently increase your strength if you cut it's heads off. There's also a trap table and a teleport table, making this one of the most varied and detailed mini solos I've played.
One minor problem I had, however, was that the directions tend to lead in bizarre direction. I always map my solos when playing and I was finding that a room in the south east of the dungeon somehow linked to a room in the far north in the text. This could get annoying for keen rpg cartographers.
Hidden Halls is a much more exciting solo than Gorgon. The variety of enemies and traps as well as the arena and logic areas make for a brilliant game of T&T.