Dragonstone is the name of the island located at the entrance to Blackwater Bay and the castle thereon, which was shaped from stone to look like dragons. Dragonstone was the original seat of House Targaryen in Westeros, which had been colonized and fortified as the westernmost outpost of the Valyrian Freehold.
After the Targaryen conquest of the Seven Kingdoms, the island in the newly created crownlands served as the seat of their heir apparent, known as the Prince of Dragonstone. After Robert Baratheon overthrew the Targaryens, he gave the island to his brother Stannis, creating House Baratheon of Dragonstone. This house went extinct in the year 300AC, when Loras Tyrell took the castle, later giving it to the invading Aegon VI Targaryen. Since then the castle and island have resumed their original function of serving as the holdfast of the heir apparent to the Iron Throne.
The castle has a dark reputation.