Mind-Benders of Buddhist History
One teacher, two epic voyages — to Sumatra, then over the Himalayas
Before he ever went to Tibet, the Indian master Atiśa is traditionally said to have sailed to Suvarṇadvīpa (Sumatra) and studied there for about twelve years under the teacher known as Serlingpa. Decades later, in 1042 CE, he crossed the Himalayas into Tibet at roughly the age of sixty; he never returned to India, dying at Nyethang near Lhasa in 1054.
How we know
Atiśa Dīpaṃkara Śrījñāna, b. c. 982 CE (Bengal); c. 12 years in Suvarṇadvīpa/Sumatra under Dharmakīrtiśrī (Serlingpa), returned to India c. 1025; arrived Tibet (Ngari) 1042 CE at age ~60; d. 1054 CE at Nyethang near Lhasa (Wikipedia; Treasury of Lives).
One of many fact-checked wonders across eight traditions at The Spring of Wisdom.