Welcome, I visit Malaysia regularly and keep planning to go to Indonesia but never quite make it.
The plan is to fly to Medan and visit Lake Toba, and then a lake on Samosir island.
A lake in an island on a lake in an Island
Then go on to Berestagi and enjoy some hiking up Sibayak Mountain and Sinabung Mountain!!
Hopefully the volcanoes will be only mildly active
Sadly this plan is still in abeyance!