The Underground Passage is a secret passageway underneath the New Parm Church on the Elencia continent in Grandia. The passage can only be accessed from the storeroom behind the church and only after Feena has been taken by Pakon and Chang. Justin and Sue travel through the passageway in order to stop the impending wedding of Feena and Pakon.
Pakon abducts Feena with the intention of marrying her at New Parm Church, in an effort to stop him, Justin and Sue follow them but are prevented from entering the church. The party find a storeroom at the back of the church that leads to the church via the Underground Passage.
Justin and Sue travel the passageway and end up in one of the side rooms of the church. From here, Justin and Sue enter the church from the rafters in an attempt to stop the wedding of Pakon and Feena.