You must complete a quest to gain access, handing three brands to the Guardian Statue at 64.6S 44.1W in Graveyard. See the Castle of Lord Mhoire Quest for details. After handing the brands a shortlived portal appears next to the statue that only the hander can use. On repeat visits simply use the statue to summon the portal. The courtyard is a floating platform and there are portals to the four towers of Mhoire Castle. Spectral Fountains can appear randomly in place of a creature spawn on the platform. The surface portal returns you to a bunker in Graveyard (64.7S 43.9W).