The Island fortress has a castle perched upon the cliff face with a stone bridge taking you inside. You can see the three dragons flying above the castle; Drogon, Rhaegal and Viserion.
Dragonstone is the castle that stands upon the eponymous island located in Blackwater Bay. It is the ancestral seat of House Targaryen and was the stronghold of a cadet branch of House Baratheon.
At the time the series begins, it is held for King Robert Baratheon by his brother, Lord Stannis. The Chamber of the Painted Table is inside the castle. The castle was built using advanced Valyrian stonemasonry techniques, long since lost. As a result it has many exotic features unique in all of Westeros, including massive dragon-shaped gargoyles. The entire castle is dominated by dragon motifs and reliefs. Unlike the richly-decorated and extravagant Red Keep in King’s Landing, Dragonstone is sparsely decorated and has a rough, austere appearance; its function is as a military base, not as a palace.
The castle itself is very strong, due to its advanced Valyrian design, which combined with its isolated location make it an ideal redoubt and refuge – first for the Targaryens, and for its last known lord, Stannis Baratheon. Because of these features and its geographic position, it is extremely difficult to breach and can be held by a relatively small garrison against a vastly larger force.