Well of Souls

The Well of Souls is the source of Horance the Liche's power in Ultima VII, located in Skara Brae inside the Dark Tower. The magical well essentially imprisoned most of the souls of the people of Skara Brae (even the ones that already had been dead at the time), and Horance was using it to keep up his power level to slowly drain the souls of their energy.

In Ultima VII the Avatar first had to use the Soul Cage with the well to give it power by taking some form the souls within. Mordra admitted that this was rather brutal and heartless, but that the souls would recover from it and the sacrifice was worth it to ensure their freedom. After the Liche was destroyed, it needed the final sacrifice of a ghost to destroy the well and set the souls free.

Only after everyone else declined did mayor Forsythe do the sacrifice to atone for his error that had caused the destruction of the city, destroying the Well of Souls in the process.

In spite of this, the Well of Souls reappears in Ultima IX in the ruined Skara Brae, now housed in a huge temple. The Avatar uses it to enter the Spirit Realm and ends up in a ghost version of Skara Brae where helps tormented spirits to find peace. This is also where he finds Shamino who had entered the Spirit Realm to find out the true nature of the Columns and the Guardian.

Trivia

 * One of the souls in the well is Marney. This is the very reason why Quenton won't make the sacrifice, out of fear of hurting her.
 * That the well appears in Ultima IX can only been seen as another error, as it was clearly destroyed in Ultima VII.
 * The Well of Souls also appeared in the infamous Bob White Plot of Ultima IX, but rather than leading to the spiritual realms, it involved the Avatar descending into the hole created by its destruction in Ultima VII inside the remnants of Horance's tower and to a place called the Catacombs of the Angry Dead. It also housed one of the Guardian Columns.
 * The real-world "Well of Souls," found in Jerusalem, is thought by some to be the last resting place of the Ark of the Covenant. It was seen theatrically (though relocated to Tanis, Egypt) in the movie Raiders of the Lost Ark.