Answering your query, I can list out some of Nepal's historical destinations and monuments which are,
i) Lumbini - Believed to be the birthplace of Gautama Buddha.
ii) Bodhanath Stupa - Dated as old as from 6th century, it is one of the tallest in the world in its kind.
iii) Swayambhunath Temple - A religious architecture on the top of a hill in Kathmandu valley.
iv) Kathmandu - Ancient cultural city and capital of the country of Nepal having lots of historical and cultural monuments, like temples, palaces, etc.
v) Bhaktapur - Residing on the old trade route to Tibet, this place is known for its red, cobble-stone streets.
vi) Patan - Nepal's most fascinating temples and palaces are here in this place. Famous for its traditional ancient guest houses and shops which sells unique handicrafts.