This large image of a castle at the top of a cliff, high in the clouds is available as both a SVG and png.
A beautiful clipart castle has towers topped with vibrant red roofs and bright pink / fushia flags flying high. Since it's a transparent png the edges will look nice and smooth in modern browsers.
Here's a smaller, more foreboding looking one, high atop a rocky hill.
A tiny image of a brown castle with 2 turrets.
Tiny image of fortified walls topped with battlements.
This one looks more like something from a fairy tale to me with its pink walls and bright blue turret tops.
Castle sitting on a cloud.
A gold castle on top of a hill.