Sunspear

Sunspear is the capital of Dorne, the southernmost of the Seven Kingdoms, located in the far southeast of the continent on the Summer Sea. It consists of a strong, fortified castle and a town that sprawls around it. It is a town built largely of mud and straw. The town's largest structure is  the Spear Tower, a 150-feet structure with a pinnacle of shining steel.

The castle was the seat of House Martell, the Princes and Princesses of Dorne.

In the books
In the A Song of Ice and Fire novels, Sunspear is the principal stronghold of House Martell. It is located on the far-eastern coast of Dorne and consists of two strong towers, the Spear Tower and the Tower of the Sun, the latter of which contains the Prince of Dorne's throne room. The castle walls are sand-colored, setting it apart from the other major castles of Westeros.

Sunspear is surrounded by the shadow town, which consists of shops, markets and bazaars. The town is also walled, though more buildings - mostly mud-brick hovels - stretch beyond it. The castle and town also have a modest harbor. Areo Hotah, who is from the Free Cities, notes that the town around Sunspear isn't really large enough to be considered a true "city" on the scale of Norvos, Pentos, or King's Landing, but it is still the largest settlement in Dorne.