I think this is the only actual opium den that I have ever seen. The guide said that the bottom bunk cost more than the top because it was closer to the floor.
from The Portland Underground FAQ:
"The victims were held captive in small brick cells or makeshift wood and tin prisons until they were sold to the sea captains. A sea captain who needed additional men to fill his crew notified the shanghaiiers that he was ready to set sail in the early-morning hours, and would purchase the men for $50 to $55 a head."