Bullbone Island
From The Fifth City Wiki

Bullbone Island is part of the Southern Archipelago. It's known for its glim, mandrakes and beetles. It is hinted that it may have been part of the First City. The island has only one human resident, a recent exile from London who chose to leave after discovering a court secret.
London's most Watchful visit and explore as part of the Dilmun Club's scientific expeditions.