When she died, everyone who knew her felt great sorrow.
--Gunhilda's Famous Wizard Card
" ...this one here, this one leads right into the cellar of Honeydukes. We've used it loads of times. And as you might've noticed, the entrance is right outside this room, through that one-eyed old crone's hump."
-- Fred Weasley, showing Harry the Marauder's Map (PA10)
Gunhilda was a one-eyed, hump-backed witch who was a beloved healer in the 16th Century. Gunhilda is known for developing a cure for Dragon Pox (FW). A statue of Gunhilda stands in the corridors of Hogwarts; a secret passageway leading to Honeydukes’ in Hogsmeade opens with a door in her hump (PA10).
This witch's name may be based on that of Gunnhildr Gormsdóttir, a quasi-historical medieval Norwegian queen who spent some of her life in exile in the Orkney Islands (source: Wikipedia).
Gunhilda's Famous Wizard Card: