The Sakala Center, built in 1985 as the central conference point for the Communist Party, was known colloquially as the Karl's Cathedral (Karl Marx in this case, and a counter-reference to the medieval catholic St. Charles Church, not too far away). It housed training facilities as well as a massive main hall; like many other 1980s Soviet public buildings in Tallinn, its architecture was about sensation rather than function; it was intended very much as a tribute to the grand power of the state.
Sakala Keskus now has a special significance as that very rare thing - a decidedly Soviet symbol that modern Estonians enjoy having around. When the government gave permission for redevelopment of this location, and the winning bidder unveiled plans to tear down the entire compound, it caused an uproar among the general population. The developer actually took out centerfold ads in full color in the major newspapers, defending the plans for the new mall. But eventually the Tallinn city government was forced to renegotiate its planning permission. The corner tower marking the entrance to the old Sakala Center, a gray tower vaguely reminiscent of a Flaktürme will be incorporated into the new structure, as will some other parts of the compound.
Karl's Cathedral is, it seems, one Soviet memorial that 21st century Estonians would like to keep.