Books like The Forbidden Tower
Marion Zimmer Bradley
The Forbidden Tower is 368 pages, about 6 hours 45 minutes at 250 words a minute.
12 books to read next
How long each takes
A Game of Thrones 14.7 h 
The Midnight Library 5.6 h 
Before the Coffee Gets Cold 4.4 h 
The Gunslinger 4.8 h 
American Gods 10.6 h 
Annihilation 3.8 h 
Animal Farm / Nineteen Eighty-Four 6.6 h 
Children of Dune 9.2 h 
The Passage 16.6 h 
Storm Front 6.5 h 
Cloud Atlas 10.0 h 
A Princess of Mars 3.2 h Bar height shows length. Estimated at 250 words a minute.