I started with "In Our Time", recommended for the quality of the guests, the variety of subjects and number of episodes (near 900)
At the moment I switch between these 3:
"The Age of Napoleon" (https://podbay.fm/podcast/1223795973) and "Revolutions" (https://podbay.fm/podcast/703889772) rekindled my interest for History, especially the 19th century.
"The History of Literature" (https://podbay.fm/podcast/1048375034)