Batman: Return to Arkham - Arkham Asylum

This achievement will unlock once 204 of the 240 riddler challenges have been solved

Press LB for XRay Vision Look for Trophies, Chronicles of Arkham, Interview Tapes, Chattering teeth.

When you enter an area a riddle will appear solve the riddle by focusing on an object and holding LB

Once you unlock the secrets of the map then the riddle locations appear on the map.

Here is a guide if you are struggling with any riddles.
Start this ASAP otherwise you will spend hours trying to solve them.

http://www.gamesradar.com/batman-arkham-asylum-riddler-guide...