Mahabodhi Temple, Chinese Temple, Bodhi Tree
These are three must visit places. The Mahabodhi temple is an architectural marvel and it is unique in that it is also visited by Hindus apart from Buddhists because the temple complex houses a 9th century Shiva Linga. The beauty of the carved and sculpted votive stupas inside the complex will amaze you. The Bodhi tree traces its lineage to the original tree under which Lord Buddha attained enlightenment and is to the south of the Temple. In close proximity to the Mahabodhi temple you will find the Chinese Temple erected by Chinese monks using typical Chinese architectural style and design.
Vishnupad Temple
The temple is dedicated to the footprint of Lord Vishnu, whence the name. It is about 40 cms in Length and the complex also houses shrines to other deities, with that of Lord Shiva to be found in the eastern side. A dip in the neighboring Surya Kund is said to free you of all sins.
Barabar Caves and Dungeshwari Cave Temples
Tour of Gaya is incomplete if you do not take the trouble to visit Barabar Caves and the Dungeshwari Cave Temples. This is where the Buddha spent years in meditation before he headed towards Gaya. The Barabar Caves date back to 322BC or even earlier, said to have been used by Hindu, Jain and Buddhist Sadhus as can be testified by the presence of Jain and Hindu sculptures inside as well as Buddhist inscriptions. The carvings are simply fantastic.
Thai Monastery, Indosan Nippon Japanese Temple, Royal Bhutan Monastery
The King of Bhutan had this monastery constructed and it has an aura of peace and serenity. The Indosan Nippon Japanese temple about 15 km from the city is a marvel of Japanese art and has beautiful wood carving. The Thai Monastery has unique looks and it is famous for its large prayer hall. You will also find it of interest to visit the Tibetan Monastery. These temples give insights into how various countries have adapted Buddhism.
There are other places of interest to Muslims such as the Baitul Anwar, shrine of Hazrat Makhdoom Syed Shah Darwesh Ashraf and Jama Masjid located in and around Gaya.