During the Soviet era, which place served as a repository for political dissidents and troublemakers?

If we're talking Stalin, it'll be gulags.

Following Czarist repressive traditions, Soviet dissidents, "troublemakers" and innocent victims of repression were sent to Siberia. That practice, with varying degrees of consistency, went on until the 1980s. The imprisonment of Russian oligarch Mikhail Khodorkovsky, who served his sentence in a prison in Siberia, shows that the practice continues today.