The SANS Pen Test group has a poster they hand out at SANS conferences and put in mailings that has an awesome mind map of hacking challenge/skills sites.
Won’t be going to conference soon or not on the mailing list? No worries, the poster can be downloaded here and all of the SANS posters are located here, including DFIR, Threat Intelligence, CIS and some general information posters.
If you’re not familiar with SANS posters, they’re not just marketing tools (but of course they advertise an event, too) but are full of good, useful information. Like the hack sites mind map.