The Grandest Tour

Needs Tours & Tournaments and an empire with ten king-tier vassals - which you may have to manufacture: granting kingdom titles to loyal family members is the quick route if your realm is short of crowned heads. Then one Grand Tour visiting all ten courts; budget for the long itinerary and run it while at peace. The wiki's favourite setup is the aftermath of Bod Chen Po: with the Empire of Tibet formed, vassalise into India and the kings pile up fast.