Final answer:
Agatha found the portal to the Halfway Bridge in the Gothic portal of a church, which is an entrance covered with sculpture.
Step-by-step explanation:
Agatha found the portal to the Halfway Bridge in the Gothic portal of a church. In Gothic architecture, portals are entrances to churches and typically have sculptures and carvings with religious symbolism. The Halfway Bridge portal is described as being covered with sculpture, with sculptures within the archivolts and a tympanum at the top.