Hi, I´m back in the morgue after a long, long way. Now I shall find the portal in here, but I can´t. Does anyone know where to find it?

Thanks a lot

The portal you're looking for can be located just north of the slab you've started the game from. The same room where you meet Morte... just go all the way north till you hit the fence with that botomless hole and the option to open the portal will be presented to you.

A warning though... restock with a lot of blood charms and other stuff you might need. You most likely won't be coming back to Sigil.