Happy that you enjoyed Galle. Sri Lanka is one of the most denser UNESCO world heritage sites containing country. All to gather it has 8 World heritage sites.
The Sri Dalada Maligawa or The Temple of the Sacred Tooth Relic in Kandy
Sigiriya Rock fortress in Dambulla
Ancient City of Anuradapura (one of the longest inhabited places in the world)
Galle Fort
Ancient city of polonnaruwa
Dambulla cave temple
Sinharaja rainforest
Central Highlands consisting of Hortan plains and Knuckles Forest
Don't miss any of these sites during your next visit.