Synagogues have an Ark (Aron HaKodesh or heichal) to hold Torah scrolls.
This ark commemorates the Aron HaB’rit or Ark of the Covenant, which contained the original stone tablets of the Ten Commandments.
The ark is usually on the wall of the synagogue which faces towards Jerusalem. Some are free-standing.
It is typically only opened during special prayers or when taking out a Torah to read.
Arks can be decorated in lots of different ways. Many have a curtain covering the front and the tablets of the Ten Commandments at the top.
Text adapted from Simple English Wikipedia, Creative Commons Attribution-ShareAlike License 4.0.
New Synagogue Darmstadt by Brian Clarke on Wikimedia Commons, CC-BY-SA 4.0.