The Taj Mahal is flanked by two identical structures. One of which is a mosque and other one is it’s Jawab (Answer).
The mosque is situated in west side and Jawab is on eastern part. The structures are made of Red Sandstone. Structures are identical in shape, size, design but one of them is used as Mosque for prayer. The Jawab does not have the Mihrab hence it does not show the direction of Kaaba so can not be used for Prayers.
Mihrab is a wall of mosque that indicates the direction of Qibla.It is the direction of Kaaba in Mecca and muslim face that side for prayers.
The structures are 64 meters in Height and 24 meter wide. These have 3 dome with 4 octagonal towers. The domes are made of Marbel hence are white.
The mosque design is very similar to Masjid-I-Jahan-Numa(Jama Masjid, Delhi). Both the structures have enormous vaulting dome.