Vormir

"Where is the Soul Stone?" "Vormir! The Stone is on Vormir."

- Thanos and Gamora

Vormir is a remote barren planet, where the Soul Stone was located.

New Guardian
In 1945, the Red Skull was transported by the Space Stone to Vormir, where he became the keeper of the Soul Stone.

Gamora's Investigation
Gamora came to learn of Vormir and its housing of the Soul Stone, keeping this information a secret from her estranged, megalomaniac father Thanos.

Sacrifice of Gamora
Eventually being forced to reveal the location of the Soul Stone, Thanos took Gamora to Vormir to find it. Reaching the mountains, they were greeted by the Stonekeeper. He explained that the only way to acquire the Soul Stone was to give up one's "soul", but it had to be the soul of someone he loved. Gamora laughed saying that Thanos never felt a thing for anyone but himself just to find him crying, as he pulls her into the abyss and so Thanos sacrificed Gamora in anguish, weeping for her, while earning the Soul Stone for his Infinity Gauntlet.

Trivia

 * In the comics, Vormir is the sixth planet in the Helgentar system, and home to the Vorms.

Behind the Scenes

 * The scenes that took place in Vormir were shot in in, Brazil. The shootings lasted for two weeks and as part of a confidentiality agreement, the project was called "Mary Lou" to keep them a secret.