by Gary Gygax
This Sample Level is the immediate ancestor of the Sample Dungeon in the Holmes Basic rulebook. In creating the Basic rulebook, Holmes generally tried to retain the words of the original D&D rulebook. While this Sample Level was replaced completely with the Zenopus dungeon, he obviously felt the concept was an important feature to retain in a beginner's rulebook. It's easy to see why Holmes replaced this Sample Level; it's not perceivably geared toward beginners, being more of a collection of dungeon features and tricks that the DM can use with more experienced players.
The map for the Sample Level is found on page 4 of the third volume of the original D&D set, Underworld & Wilderness Adventures, and includes 8 numbered and 8 lettered locations. Page 5 then follows with a section titled "Sample Map of Underworld Level" which describes the numbered and lettered locations.
Two different versions of the map exist in different printings of the OD&D set. The first version is the rougher version shown to the left. This was replaced in later printings with a map that is more polished but renders the features confusing. The key remains unchanged, but despite this many of the features of the map no longer correspond to those shown in the key. For example, despite having an "Under Floor Passage" in the key, the revised map no longer shows the passage from the pit to location I. The revised map also incorrectly shows the pit as a "P" rather than an X as described in the Key and in the description of location 8 of the text.
Some OD&D Discussion Threads about this level:
The First Published Dungeon
Sample Floor Plan Re-created (redrawn by piper using Autorealm)
The original drawing of the Sample Level, page 4 of Underworld & Wilderness Adventures,
as scanned and posted by T. Foster at OD&D Discussion