*This Achievement Should no longer be glitched if you've beaten the dark room before the patch just start a new run and your achievement will unlock*
To get to the Dark Room, you must first beat Satan in Sheol, 5 times unlocking the Negative. When you beat mom she drops the Negative. when you beat moms heart go down into Shoel, beat Satan, walk into the chest and be taken to the dark room. The first room of the dark room has 4 red chests. they can have spiders, fly's, pills, spirit hearts. Every other chest you find will contain a free Item. Make your way to the boss room Kill the Lamb, then walk into the chest he spawns, and unlock your achievement.