you have to fight your way thru the fort leading to pagan .. take over several locations .. then blow up the golden statue of pagan .. then blow open the doors with explosives .. yes you need to blow open doors a few times .. ti get to the top to the statue ..fight off all reinforcements .. then blow open the final gate .. then driver up the rod to pagans home
go watch some videos online on youtube if you get stuck
https://www.ign.com/wikis/far-cry-4/Ashes_to_Ashes
is the name of that mission before you confront pagan