Ideas to change terrain symbols to reduce overcrowding of the # symbol:

• Iron bars and fences render as cyan or brown wall glyphs.
• Sinks render as white or blue \.
• Closed drawbridges render as some color of + which is not used by many spellbooks - perhaps red or orange.
• Corridors could be moved to a period glyph but this would probably be very unpopular and make levels look a lot worse.
• Trees could be green +, or possibly green \ to avoid spellbook confusion.
• Clouds could set the background color of a space and not change the foreground color, and could possibly be rendered with a blank space character, but this would probably have issues on non-color terminals.