'''Arkin's Castle''' ({{lang-ga|Caisleán Aircín}}) is a 13th-century ruined castle on the island of [[Inishmore]], [[County Galway]], [[Ireland]]. It is owned by the [[Department of the Environment, Climate and Communications]] of Ireland.<ref>https://digital.nli.ie/Record/vtls000737502/StaffViewMARC</ref><ref>https://www.archaeology.ie/sites/default/files/media/pdf/monuments-in-state-care-galway.pdf</ref><ref>https://www.logainm.ie/en/1397430</ref><ref>https://www.patrickcomerford.com/2019/07/arkins-castle-struggles-to-survive-on.html</ref>

Likely built by the [[O'Brien dynasty|O'Brien family]] in the 1200s, it passed through various owners in the 16th and 17th centuries, including [[Teige Ó Flaithbheartaigh]] in 1607. By the 1650s, the original structure had been demolished and a new, enlarged fort was built for [[Oliver Cromwell]], where he stationed soldiers throughout the 1660s. Since the 1700s, it has been uninhabited. Today the ruins include part of a wall and water-gate to the north, a tower at the south-east corner, and a [[bartizan]].<ref>https://digital.nli.ie/Record/vtls000737502/StaffViewMARC</ref><ref>https://visionsofthepastblog.com/2018/11/19/church-of-st-thomas-inishmore-galway-ireland/</ref><ref>https://irishantiquities.bravehost.com/galway/inismor/arkinscastle.html</ref><ref>https://www.patrickcomerford.com/2019/07/arkins-castle-struggles-to-survive-on.html</ref><ref>https://www.aranislands.ie/aran-islands/aran-islands-culture-history/military-monuments</ref>

The castle is listed on the [[Record of Monuments and Places]] as ''GA119-005----'' and [[National monument (Ireland)|National Monument number]] 43.01.<ref>https://www.archaeology.ie/sites/default/files/media/pdf/monuments-in-state-care-galway.pdf</ref>