You are probably going to have to use the word "similar" loosely as there is no other city quite like Amsterdam I'm sure.

Talking about weed and girls here gents. Any recommendations? Thaland looks pretty amazing with regards to the girls but I believe they are are strict on marijuana laws there and that it's super corrupt.

Prague and loads of cities Germany (Stuttgaart, Cologne, Hamburg).

And besides loads of coffee shops are being clamped down in Amsterdam, it's not what it used to be. But Europe is pretty is easy to get around and if you're travelling from US, any other city in Europe is usually only 1-2 hours extra flight time.

It's the combination that makes it hard to find a "similar" city. (1) Windows-style prostitution (2) functionally legal weed in coffeeshops (3) both (1) & (2) embedded in a pleasant neighborhood where there are intermingled options for food, drink, and shopping.

(2) you won't find outside of the Netherlands. And in other NL towns you are less likely to find the (3) neighborhood mix...the RLD may be somewhat isolated and monolithic.