Welcome to heaven. This is my favorite place in Earth. I stayed a week and wish I could have stayed longer! Lake Toba is a huge freshwater lake. Although it's not far from the equator, the temperature is very mild because of the elevation. You will most likely begin your stay in Parapat, a small village on the eastern shore of the island. From here you will take a boat to Samosir Island, which is about the size of Singapore and is home to the Batak people. Most visitors stay in Tuk Tuk, a small peninsula ringed with restaurants and hotels. I heard people complain it was touristy, but I found the place very quiet, and I was there during peak season!
WHAT NOT TO DO:
Do not run out of small bills. It is so hard to get change here! Don't run out of money period: the exchange rates are poor as well.
WHERE AND WHAT TO EAT:
When you stay at a guesthouse in Indonesia, it's understood that you'll eat most of your meals at the guesthouse's restaurant. You usually can't go wrong, though you'll find that if you ordered something one day and loved it, you'll order it the next day and it'll be disgusting! For some reason avocados are everywhere here, so you'll find tasty guacamole. There are plenty of restaurants in Tuk Tuk, where you can find the native cuisine, western food, and other goodies from carrot cake to wood fired pizza.
WHERE TO STAY:
There are lots of guesthouses and resorts. We stayed at Lekjon, and glad we did. The rooms were clean, the staff was nice and a lot of fun, and it was cheap. Our room was about three dollars a night, though that was in 1996. When you take the boat from Parapat, it'll stop at the lakeside hotel of your choosing. You should be able to bargain for a good rate as there are plenty of places to stay. The clerk at Lekjon was willing to cut some branches off a tree so it wouldn't block our view of the lake! We told him it wasn't necessary, of course, but as you can see, they are fairly accomodating here.
WHAT TO SEE:
Ambarita, just north of Tuk Tuk, has a group of stone chairs where those who did wrong had their heads cut off and were then consumed. In the village of Tomok, if you can free yourself from the tacky souvenir stalls, is the Tomb of King Sidabatu, the last animist king before Christianity arrived. Throughout the island you'll see Christian tombs dot the countryside. If you're up for a trek, you can hike across the island from Ambarita to Pangururan.
WHAT TO DO:
Swim! The water is awesome. I don't think I showered once when I was there. Rent a motorbike for the day so you can explore around the island. It's simply beautiful. The hills are gorgeous and you'll be greeted by friendly, curious people. Try to get to know the the locals; you'll find the Batak people very welcoming and a lot of fun. I don't endorse drug use, but you'll probably see magic mushroom omelets on the menu, and it seems that 90% of the men want to sell you doobie. Our hotel was serviced by a guy who delivered magic mushrooms on his canoe! Do this at your own risk, though I understand that if you're going to experiment, this is the place to do it. Few places are safer.