Pulau Penyenget, reached by frequent boats (7000Rp) from the Tanjung Pinang pier, was once the capital of the Riau rajahs. The ruins of the old palace of Rajah Ali and the tombs and graveyards of Rajah Jaafar and Rajah Ali are signposted inland. The most impressive site is the sulphur-coloured mosque, with its many domes and minarets.
The beautiful fairy-tale castle of a mosque that is the Masjid Raya Sultan Riau was built in 1832 and is painted in pastels of yellow and green. Its minarets are topped with tall conical spires and are almost Gothic Revival in style. This is an active mosque, and although visitors are welcomed, appropriate clothing should be worn; cover yourself up, or else admire the building from afar.
Penyenget was the royal capital of the Riao-Johor sultanate, and the island is dotted with the ruins of the palaces and tombs of these Malay rulers. Ones to look out for on your wanders include the ruined palace Astana Kantor, straight on from the mosque, and the tomb of Raja Hamidah, off to the left of the mosque. There are many others that you'll stumble across as you walk around the island.
At the far west of the island are the ruins of an impressive stone fort, built by the sultan Raja Haji in the 18th century to fend off Dutch attacks. Ironically, the cannons you see here are Dutch made. Raja Haji, incidentally, was the author of the first Malay grammar book, a reminder that this island was once a hotbed of intellectual and religious minds, and at one time was home to more than 9000 people.
The best way to get around the island is by motorised tricycle; expect to pay between 30,000Rp and 50,000Rp for a day trip.