Laos, Vietnam, Cambodia, Malaysia, Sri Lanka - heat
You can find cooler places everywhere:
Laos: Phonsali
Cambodia: Ratanakiri, Mondulkiri
Malaysia: Cameron Highlands
Vietnam: Sapa
One could even add Dali, Lijiang, Shangrila (Yunnan, China)
But wasn't the topic about 'tropical places'? Aren't they hot by nature?