Basic Blade Mistress Information:
The labyrinth - the only place where you can obtain chitin ingots (as boss drops and ultra rare mob drop) as well as chitin totems and plain rainbow eggs.
You enter the labyrinth via portals scattered across the normal realm, they will have a similar appearance to the exits from dungeons; a green swirling vortex that will teleport you into the lab.
Pick/find a portal, step into it and you'll be ready to enter the lab.
For those who can't work it out the co-ords in brackets after the location are the co-ords for that lab portal in NR - not the location of the recall point/town. They are also listed in Places In Normal Realm with a little more information.