Complex sentence: The Hound Pit pub that acts as a base for the player was initially a larger structure, but filling out the interior of the pub required a lot of stairs, rooms and a large amount of climbing that made navigation confusing.
Split into simpler sentences: The Hound Pit pub, which acts as a base for the player, was initially a larger structure. Filling out the interior of the pub required too many stairs and rooms, and the large amount of climbing made navigation confusing.