As the dragon flies, the horizon isn't really that far away at all, but it still takes longer than she might expect to reach the structure. It was further than it looked, just really big.

The structure appears to indeed be a castle, a huge one, but (aside from being totally abandoned), there's something odd about it. The shape. The endless crenelations and towers form...the shape of a human, when viewed from above.

There is room to land in a courtyard in side.