Involves scaling vertical surfaces without the aid of ladders or similar aides.
Alternate name: Wall scaling
The first video game about Wall climbing was released in 1980.
Easiest way to spot these is that the game allows you to climb _any_ wall or vertical surface that matches some very basic criteria, such as having small ledges or anything else to take hold of. If these are found only in few select places like ladders, then they should not be considered.