I just stumbled upon this site that has level overviews of hundreds of games.
Example of what I exactly mean:
It's pretty cool for checking out secret places, looking up where certain enemies are, that kinda stuff.
Tons and tons of games are feautured on pretty much any console (though you'll have the best luck when you look for a bit older games, 2d era).
So yeah, thought I'd post it here, someone might enjoy looking up some games for whatever reason lol
http://www.vgmaps.com/