The Soltoth Caverns were an underground volcanic region deep within the Romulan homeworld.

The caverns were inaccessible by foot and required the use of a Transporter in order to enter the underground region. The area was home to the Soltoth Command Post, a bunker facility that dated before the Earth-Romulan War and to the time when the young Romulan Star Empire fought the Hiram Assembly. At first, the Romulans were losing the conflict with the enemy entering the outskirts of the Romii system. It was decided that the Soltoth Command Post would serve as the command and control base for the Star Empire where it would direct the Imperial Romulan Fleet against its enemies. However, the war never reached Romulus itself and the caverns were abandoned.

One year after the Dominion War, Ambassador Spock faked his death on Romulus in order to help improve the progress of the Unification movement. During his assassination, Spock was transported to the Soltoth Caverns in order to await for the aftermath to see if it would improve his efforts at Reunification. However, his base of operations came under assault from Cardassian mercenaries that took him away to their employer. (TOS novel: Captain's Blood)

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