From [wiki=002d58e7320e036561568d54ac4b17ae]Medan[/wiki] there is a local bus (no air-con) about every hour for 32,000 rupiah (Feb 2014) if you pay on the bus. The journey takes 4-6 hours, depending on the traffic condition.
There are also several mini buses plying for IDR60,000 per person. If you are carrying heavy luggage, you might be asked to buy one extra ticket for the luggage.
From [wiki=002d58e7320e036561568d54ac4b17ae]Medan[/wiki]:
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*Raja Taxi ☎ +62 617 366 555
Sibisa Airport is the closest airport to Prapat, however the short runway only for very light aircraft. Silangit Airport is close to [wiki=dfe63203e038ab51f5b16d605ec160ce]Balige[/wiki], may be accessed by Wings Air from Batam.