The Lacuy Peninsula (Spanish; Castilian: península de Lacuy), alternatively spelled with i, is located in the northwestern corner of Chiloé Island. The peninsula lies a few kilometer west of Ancud but the isthmus that connects to the rest Chiloé Island lies more than 10 km west of Ancud. During colonial times, the peninsula hosted a Spanish fort system consisting of three batteries, one sentinel outpost, and one fort. The fort, named Fuerte de Agüi, was the site of the battle of Agüi in 1820.[1] The geological Lacui Formation is named after the peninsula.