Sigiriya

Sigiriya, considered by some as the eighth wonder of the world, consists of an ancient castle used by King Kashyapa of the 5th century AD.The Sigiriya site has the remains of an upper Sky Palace sited on the flat top of the rock, a mid-level terrace that includes the Lion Gate and the Mirror Wall and the Sigiriya Frescoes, the lower palace that clings to the slopes below the rock, and the moats, walls and gardens that extend for some hundreds of metres out from the base of the rock.

https://en.wikipedia.org/wiki/Sigiriya

Polonnaruwa

The second most ancient of Sri Lanka's kingdoms, Polonnaruwa was first declared the capital city by King Vijayabahu I, who defeated the Chola invaders in 1070 CE to reunite the country once more under a local leader.The ancient city of Polonnaruwa remains one of the best planned archeological relic sites in the country, standing testimony to the discipline and greatness of the kingdom's first rulers.

https://en.wikipedia.org/wiki/Polonnaruwa

Anuradhapura

Anuradhapura is the first ancient capital of Sri Lanka which lasted for the longest period as the capital in the country. It is important to locals for religion, history, and the culture and world-famous for its well-preserved ruins of the Great Sri Lankan Civilization. this ancient city of Sri Lanka, which is sacred to the Buddhist world, which its surrounding monasteries covers an area of over 40 square kilometres  and is one of the world's major archaeological sites

https://en.wikipedia.org/wiki/Anuradhapura

Tooth Relic Temple

The Temple of the Sacred Tooth Relic is a temple in the city of Kandy in Sri Lanka. It was built within the royal palace complex which houses the tooth relic of the Buddha, a tooth, which is venerated by Buddhists.The relic has played an important role in the local politics since ancient times, it's believed that whoever holds the relic holds the governance of the country, which caused the ancient kings to protect it with great effort. 

Sinharaja Forest

Sinharaja Forest Reserve is a national park in Sri Lanka. It is of international significance and has been designated a Biosphere Reserve and World Heritage Site by UNESCO.The hilly virgin rainforest, part of the Sri Lanka lowland rain forests ecoregion, was saved from the worst of commercial logging by its inaccessibility, and was designated a World Biosphere Reserve in 1978 and a World Heritage Site in 1989. 

Rock Cave Temple

Dambulla Cave temple is a world heritage site (1991) in Sri Lanka, situated in the central part of the country.preserved cave temple complex in Sri Lanka. The rock  There are more than 80 documented caves in the surrounding. Major attractions are spread over 5 caves, which contain statues and paintings. This paintings and statues are related to Lord Buddha and his life. The later 4 include two statues of Hindu gods, god Vishnu and god Ganesh.  Depictions in the walls of the caves include Buddha's temptation by Mara (demon) and Buddha's first sermon.

https://en.wikipedia.org/wiki/Dambulla_cave_temple

Galle

Galle is a town situated on the southwestern tip of Sri Lanka.Galle was known as Gimhathiththa  before the arrival of the Portuguese in the 16th century, when it was the main port on the island. Galle reached the height of its development in the 18th century, during the Dutch colonial period. The Galle fort is a world heritage site and is the largest remaining fortress in Asia built by European occupiers.

https://en.wikipedia.org/wiki/Galle