A planet concealing a huge ancient structure that proves to be a prison for the malevolent Vezda, explored in the Strange New Worlds third-season episode Through the Lens of Time.
Vadia IX is the site of a cloaked ancient complex which the archaeologist Roger Korby hopes will hold the secret of immortality. In Through the Lens of Time, a landing party from the Enterprise joins him, guided by N'Jal of the local M'Kroon, who is killed by the building's automatic defences.
The place is in fact a high-security prison in which beings called the Vezda are confined inside orbs. One of the orbs injures Ensign Dana Gamble, and the team is split between different planes of existence until they solve the structure's puzzle. A Vezda nevertheless gets out and hides in the ship's transporter buffer.
The planet returns in the season finale, New Life and New Civilizations. The Vezda is confined once more, and Captain Marie Batel stays there as the Beholder, the prison's permanent guardian.