Part 52 of a comparison of Holmes' manuscript with the published Basic Set rulebook. Turn to page 45 of your 'Blue Book' (page 44 for the 1st edition) and follow along...
Room RT: Rat Tunnels
Here Holmes includes an old-school "endless maze" with limitless monsters ("there is no end to the rats"). Rather than being arbitrary, this fits the undercity setting extremely well, with the rat tunnels "being dug through the soft earth of the cemetery". This also gives us a clue as to what is above this location on the surface.
I meant to mention back in Room N that Delta suggested that the rat encounters in Room N/Room RT bring to mind Lovecraft's Rats in the Walls. In a review of Lovecraft in the Comics in the zine Crypt of Cthulhu #97 (1997) - one of his last published articles - Holmes mentions that this is one of his favorite Lovecraft stories.
This area presents one of the larger divergences between Holmes' original map (above left) and the redrawn version in the Basic rulebook (above right). In the original the rat runnels have a single entrance to Room N, and another in the east-west corridor north of Room P. In the published version, the tunnels have been shifted west, with two entrances to Room N and one to a corridor to the west, which has been extended. It's not clear why this was done.
The original map fits the description of Room N better since it doesn't mention multiple entrance points for the rats that burst into the room "through the loose dirt at the north end of the room". The text of RT indicates that the tunnels intersect at Room N and and "at the northernmost corridor". In the original map this was the corridor north of Room P, but in the published version it is the extended corridor to the west of Room N. So the altered map was changed in a way that still fit the text for RT.
The tunnels are small, only 3 feet wide, requiring humans to crawl through them. Holmes gives a mechanic, not otherwise mentioned in the rules, for humans fighting in such a situation ("a minus 1 from his attack die roll"). This was changed in the published version to a -2, making it the same as the modifier for partial cover (pg 20). Holmes further notes that halflings and dwarves are not so disadvantaged.
Holmes gives chances for independently encountering a rat or treasure as the tunnels are traversed. A 50% chance of a rat every 100 feet, and the same chance for 5 gold pieces "or a piece of jewelry" every 200 feet. Notably, the jewelry is deleted from the published rulebook. This is a big change, as a piece of jewelry is worth 300-1800 gp (3d6 x 100 gp; the average value is 1050 gp) in these rules. Once again Gygax/TSR has reduced the amount of treasure Holmes placed in the dungeon. Holmes' original presents a much greater reward for entering the rat tunnels. Note that Holmes' rats originally had 1 HD as described in Room N (which the entry for RT references).
Example of a lair maze with a repeated chance of encountering inhabitants/treasure
Rules for fighting while crawling through tunnel
Go Back to Part 51: "Indescribable Odds and Ends"
or Go Back to Start: The Holmes Manuscript