I live near there and never heard about them until 2007. We went on a guided tour of them as part of a Gothic Victorian Haunted Tour of Portland. It is a pretty short tour, basically covering the interconnected basement of two restaurants/pubs in downtown Portland.

It was very much what you would expect from Slave Trade. However, Shanghai'ing 1500 people over 90 years comes out to be about 16-17 people abducted a year.

I'm sure the underground Slave Trade continued since the 1940s, and has grown far more sophisticated since...accounting for far more than 16-17 people being abducted a year.

Still, it's a dark spot on Americana. They say they are haunted, however in the 40 minutes in that dark and dirty cellar, I didn't see anything to indicate such.