The Buddhism that we know today was developed in Tibet. Therefore, Tibet is the best place to visit if you want to learn about Buddhism. However, due to the interference from mainland China, they say Buddhism is in decline in Tibet. In that case, you can visit Nepal or India to learn about Buddhism. The historical Buddha was born in Lumbini, Nepal and he attained Nirvana in Bodh Gaya, India. You can also visit Dharmashala, where the 14th Dalai Lama lives. Dharmashala is in the Indian state of Himacha Pradesh.
In case you want to travel to Nepal to learn Buddhism, you might want to visit Lumbini, where the Buddha was born. In Lumbini you will find a marker stone that marks the exact birth spot. There is also a pond where the Buddha's mother bathed before giving birth to the Buddha. The Lumbini circuit tour that takes 2-3 days takes you to various historical places related to the Buddha such as Kapilvastu, the home of Buddha, Sagarhawa the site of war that destroyed the Shakya clan (the clan of the Buddha) and Lumbini garden, the place where the Buddha was born.