The Rummelsburger Bucht is a bay around the Rummelsburg lake. While walking all around the lake, which is actually a small branch of the river Spree, you will be overwhelmed by the beauty of the Berlin skyline and the new modern and fancy houses. Those were built mostly after 1997. In the 20th century this area used to be mostly industrial.
Some of the old houses are under monument protection so they reconstructed most of them completely, for example the two “Knabenhäuser” (boys’ houses) which were part of an orphanage built under the German Emperor.
All around the bank you can find small fenced ecosystems where you can watch animals. The closest station is Ostkreuz or Rummelsburg (S-Bahn).