João Cabral (d. 1699) and Estavão Cacella (d. 1630) were the first westerners to record their journey to Bhutan and Shigatse in Central Tibet (Tsang). The ruling king of Tibet at the time, Karma Tenkyong Wangpo (Karma Bstan skyong dbang po, 1599-1642) welcomed the two men, and encouraged them to learn the Tibetan language, so they could converse more freely. They seem to have depended on Armenian traders for translation in the meantime. Cabral only stayed ten days on this first trip before hurrying south through Nepal, to find a safe route to support the mission. Cabral's letter of 1628 gives remarkably positive picture of Tibet and the king who supported them: "This King is a youth of twenty-two years, very well educated, fair, very affectionate and, above all, very generous and liberal to the poor. The royal city ... [in its] building and plan are like the ones in Portugal, and the only missing is the artillery. The homes inside are all gilded and painted, and the King's quarters are worth seeing, especially the many rooms of curios of all kinds. Because he is a very rich king, the best of everything comes to him. He uses many tapestries in all this apartments. The plainest are damask from China. The others can compare with any of the good ones of Portugal. the people who serve him dress very cleanly and can be seen everywhere....[Tsang] is so densely populated that in the twenty days I traveled from the court to the border of the Kingdom of Nepal....I always went past and through villages....They have great fields of wheat, and I never saw land that looked more like the Alemtejo of Portugal." Cacella remained in Shigatse for one and half years until June 1629. Cabral returned to Shigatse in 1631, but left again in 1632, which marked the end of the mission there. Karma Tenkyong Wangpo was executed after being taken prisoner by the joint army of Qoshot (Oirat/Kalmyck) Mongols and Tibetans supporting the Gelukpa tradition of Tibetan Buddhism.

Source: Nancy Moore Gettelman. "Karma-Btsan-skyong and the Jesuits." in Epstein & Sherburne. Reflections on Tibetan Culture. Lewiston, ME: Edwin Mellen Press. 267-277.
Other letters partially translated by Michael Aris. Bhutan: The Early History of a Himalayan Kingdom. Warminster: Aris and Phillips. 1979, Pt. 5, No. 4.
See also: Cacella's "Report on Bhutan in 1627", trans Luiza Maria Baillie in Journal of Bhutan Studies.