Complex sentence: The square is named today after the old synagogue, which was destroyed during the Kristallnacht in 1938 which had been built in 1869/1870 to the southwest of today's location of the square.
Split into simpler sentences: The square is named after the old synagogue, which was destroyed during the Kristallnacht in 1938. The synagogue had been built in 1869/1870 to the southwest of today's location of the square.