Famed Korean Buddhist Monk Hyecho (AD 704-787) of the Silla Kingdom of Korea, also known as Praj??vikram in Sanskrit and Hui Chao in Chinese, went over to China and studied Esoteric Buddhism, and toured five different kingdoms of Cheonchuk-guk (now India) and various countries of Central Asia in the 8th Century. As a result, Hyecho wrote a travelogue named Wang O Cheonchuk-guk Jeon (literally, Tales of Traveling Five Cheonchuk-guk [India] Countries).
The travelogue is considered the only written records of the customs and ways of living of the different peoples in India and various Central Asian countries as well as China.
The records include a kingdom where brothers shared one wife, a kingdom where men and women lived without any clothes on, a kingdom where there were Buddhist temples but they were empty without any Buddhist monks, a kingdom where there was a big temple with over 3,000 monks living and therefore always suffering from shortage of food, a kingdom in a northern region where the Buddhist believers were so devout that they even donated their wives and elephants, a kingdom where there was no prison but where all the criminals were fined to pay money for their crimes instead of penal servitude, a kingdom where people had no soy sauce but had only salt to cook their meal with, a kingdom where killing of any living things was strictly prohibited, and a kingdom where people cooked their ice in earthen jars.
Hyecho is known to have studied the Esoteric Buddhism initially under Subhakarasimha and then under the famous Indian Monk Vajrabodhi who praised Hyecho as "one of the six living persons who were well-trained in the five sections of the Buddhist canon."
According to Wikipedia, Hyecho set out for India in 723 CE on the advice of his Indian teachers in China to acquaint himself with the language and culture of the land of the Buddha.
The travelogue reveals that Hyecho, after arriving by sea in India, headed to the Indian Kingdom of Magadha (present-day Bihar), then moved on to visit Kusinagar and Varanasi. However Hyecho's journey did not end there but he continued north, where he visited Lumbini (present-day Nepal), Kashmir, the Arabs. Hyecho left India following the Silk Road towards the west, via Agni or Karashahr, to China where the account ends in 729 CE.
He referred to three kingdoms lying to the northeast of Kashmir which were "under the suzerainty of the Tibetans. The country is narrow and small, and the mountains and valleys very rugged. There are monasteries and monks, and the people faithfully venerate the Three Jewels. As to the kingdom of Tibet to the East, there are no monasteries at all and the Buddha's teaching is unknown; but in countries the population consists of Hu, therefore they are believers.
It took Hyecho approximately four years to complete his journey. The travelogue contains much information on local diet, languages, climate, cultures, and political situations.
It is mentioned that Hyecho witnessed the decline of Buddhism in India. He also found it quite interesting to see the cattle roaming freely around cities and villages.
The travelogue was lost for many years until a fragment of it was rediscovered by Paul Pelliot in the Dunhuang grotto in China in 1908 and was subsequently translated into different languages over the years; the original version of Wang O Cheonchuk-guk Jeon is now at the National History Museum in Paris, France.