Arcadia is a plane of existence in the D&D multiverse. Its connection to the adventure comes through a pair of magical spectacles found in the Tomb of the Nine Gods.
Portal Connection
The horn-rimmed spectacles belonging to an arcanaloth serve as a gate key that opens a portal in the planar city of Sigil. This portal functions as a two-way door between Sigil and Arcadia.
Discovery
The spectacles can be identified through a legend lore spell, which reveals their properties as a planar gate key. This knowledge significantly increases their value from 250 gp (as mere spectacles) to 2,500 gp when sold to a wizard or sage who understands their true purpose.
Adventure Relevance
While Arcadia itself doesn’t feature directly in the Tomb of Annihilation adventure, the spectacles represent a potential avenue for planar travel and could serve as a valuable treasure or plot hook for further adventures beyond Chult.