The capital world of the Tandarans, a people at war with the Suliban Cabal who interned their own Suliban citizens, mentioned in the Enterprise episode Detained.
Tandar Prime is the home planet of the Tandarans. It is talked about but not seen in the Enterprise episode Detained, set in 2152, in which Archer and Mayweather stray into a Tandaran military zone and are locked up in a detention complex alongside Suliban civilians.
The camp commander, Colonel Grat, tells Archer that he will be taken to Tandar Prime for a hearing before a magistrate, and suggests that Enterprise travel there to wait for him, even offering a tour of the capital city.
From the prisoner Danik, Archer learns that many Suliban had lived peacefully on Tandar Prime for generations. Danik himself worked at an engineering institute there before the Cabal's attacks led the government to round up every Suliban, a policy the episode compares to the wartime internment of Japanese Americans.