Generally when I want to learn something new I'll build a new side project (or re-build an existing one) to support the learning process. This time I wanted to include my partner in the project so I built something that would require some manual moderation of content.

I built a 'hookup' website and have monetized it with a single affiliate offer/link.

It's made a few thousand in the last 18 months or so, with almost no promotion (posted something about it on reddit once).

Like someone else in this post commented, the way that the 'adult' industry is pushed out of the banking/credit card world makes it pretty tough to monetize sites of this nature.