Map of the House. Take the second door on the left in the hallway with the large footprints. Inside the locker room, press the tile on the floor.
Map of the Caverns. After the Mausoleum, we revisit the Typewriter Room and take the (previously sealed) door to our right, and enter a dark room with wooden panelling, where we find the map on a small table.
With the help of the XWE Editor, we're able to access the textures and sprites of Realms of the Haunting. Taradino Cassett has kindly assembled an extractable archive of these graphics, available for download over at Doomworld.
Some of these textures have been named by the developers in most curious and interesting ways, lending us some valuable, and not seldomly humorous, insight into the creation process and the identity of certain objects and locations.
For this purpose, I've created a separate article page, dedicated to these particular files.