Babu shakka mafi girman abin tunawa a Jaca, sanannen Citadel, an san shi har zuwa karni na XNUMX a matsayin "Castillo de San Pedro", sansanin soja wanda ya fara aikinsa zuwa ƙarshen karni na XNUMX, kuma an kammala shi a karni na XNUMX. Kagarar Jaca Asalinsa an tashe shi a matsayin wani ɓangare na babban tsaro, wanda ke nufin kare manyan kan iyakokin Faransawa don haka ya dakatar da yaƙe-yaƙe na addini tsakanin Furotesta da Katolika da aka ɓarke a waɗancan ƙarni a Turai.
Ginin Gidan San Pedro Felipe II ne ya damka shi ga Injiniyan kasar Tiburcio Spanochi, wanda ya ba da shawarar samar da filayen da za a yi amfani da su, a yankin arewa na gefen garin Jaca. An gabatar da wannan katanga a matsayin babban gini mai katanga tare da shirin yanki na murabba'i, tare da gutsin mai zoben kibiya a kowane kusurwa, duk suna da alaƙa da juna ta hanyar hanyar tafiya da aka rufe.
A ciki, a cikin ɓangaren tsakiya, Citadel yana da babban filin fareti, wanda aka keɓance ta hanyar matakin arcade mai hawa biyu wanda zai canza madafun tubalin zagaye na zagaye. Hakanan ciki yana ɗauke da ƙaramin cocin da aka keɓe ga Saint Peter, wanda ya fara daga karni na goma sha bakwai, wanda ke da faɗin Faren wanda yake kusa da ginshiƙan sandunan Solomonic. A waje, an kammala tsarin karewa tare da glacis da moat a tsayi biyu, wanda bai taɓa ƙunsar ruwa ba amma wanda a halin yanzu ya zama mazaunin wasu barewa. Hannun kayan yaki na Habsburgs ya sanya ƙofar zuwa garu. An ayyana kagarar Abin tunawa a ranar 28 ga Yuni, 1951, An sake dawo dashi tun 1968.