In North Sumatra you can go trekking in Bukit Lawang, you can book it once you get there. Trekking is 25 euros for 1 day, 60 for 2, and 85 for 3. Bukit Lawang is about 3 - 4 hours from the airport in Medan, and as log as you arrive before about 4 in the afternoon you can get a taxi/minivan straight from the airport, about 30 quid, although can be done a lot cheaper, you will get assaulted by drivers as soon as you walk out, very friendly but can be a bit annoying. Medan is best avoided, although you can get a 5* hotel for about 70 quid a night.
Getting from Medan to Bali the cheapest airline is airasia if booked in advance

If the earth tremors expect to be going for an involuntary swim to Darwin soon after.

Big chest and massive boobs

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For any country that likes to tie visitors to a stump and shoot them for drug offences (or indeed any country with a propensity for drug export), I've had my luggage wrapped in the airport, both inbound and outbound.

There have been instances of handlers slipping something "extra" into your luggage before it boards. The intended recipient at the destination doesn't take it out, and you're left explaining why you just brazenly transported 2kg of coke in your luggage.

If the luggage is "clingfilm wrapped", it foremost serves as a deterrent. If you receive the luggage and it looks like it's been tampered with, the film cut etc, you can inform the authorities. Better safe than sorry.

Best Scuba diving in the world, if you are not a diver, learn before you go if you can.

I spent 10 weeks diving around Indonesia and it's an amzing place as that's where the three major world currents meet so the diversity is amazing.

Well based on all this, I can't wait to go!!

Don't watch The Year of Living Dangerously before you go.