One of the locations mentioned in Merlin's prophecy where King Arthur and his knights embarked on a quest to seek out the Sangraal, also known as the Bloodstone. The land is said to be a great distance from Camelot. (It is believed Arthur also searched for the device in Castiana and Sahal.)
Daniel Jackson discovered the Stargate symbols for Vagonbrei in a drawing of Ser Gawain's sword. Upon arrival to the planet SG-1 discovered a dead village filled with corpses, many of whom appeared to have passed away in their beds. Upon examination of a nearby cave, where it is believed Morgan Le Fay resided for a time, microscopic parasites which feed on melatonin were found.
Camelot - Meurik tells Mitchell and Jackson of Arthur's quest to seek out Castiana, Sahal and Vagonbrei.
Morpheus - Daniel discovers references to Vagonbrei in texts from Camelot, leading SG-1 to a dangerous planet.
The Quest, Part 1 - Daniel and Vala discover that Vagonbrei's gate address is only one part of a puzzle that will lead them to the Sangraal.