Banda Aceh sits at the far northern tip of Sumatra, closer in feeling to the Indian Ocean and the old Muslim trading world than to beach-resort Indonesia. It is the capital of Aceh, the province known as the "Veranda of Mecca", and it remains one of the most visibly Islamic cities in the country. Dress modestly, expect alcohol to be difficult to find, and you will usually be met with straightforward hospitality.
The city is not polished, but it is powerful. The white domes of the Baiturrahman Grand Mosque dominate the centre, while the Aceh Tsunami Museum, PLTD Apung 1, and the Boat on the Roof make the 2004 disaster impossible to treat as an abstract event. Banda Aceh was devastated; the rebuilt city carries that memory openly.
There is older history here too. The Aceh Museum and Gunongan Historical Park point back to the Aceh Sultanate, when this was one of Southeast Asia's strongest Islamic courts. The Dutch cemetery at Kerkhof Peutjoet is a sober reminder that Aceh was also one of the hardest places the colonial state ever tried to subdue.
Most travellers use Banda Aceh as the ferry gateway to Sabang Island and Pulau Weh's reefs. Give it a day before or after the boat if you can. Few Indonesian cities explain themselves so honestly.