The Sultan Abu Baker Mosque was constructed upon a hill overlooking the Johor Straits between 1892 and 1900 and is the state mosque for Johor. The mosque can accommodate 3,000 worshippers.
Sultan Abu Baker Mosque. All photos are by John Hunter.
I recommended taking a short trip to visit and walking around the grounds. You can walk to old town from without much trouble (I would guess it is less than 2 km from old town), obviously you can drive or take a taxi if you prefer.
This square building and two large rectangular buildings of the same style sit on the non-Straits side of the Mosque.