In the books
In the A Song of Ice and Fire novels, Ten Towers is the newest castle in the Iron Islands, built on the island of Harlaw. It is described as being more like ten castles smashed together. The castle was built by Lord Theomore Harlaw, who raised the castle after he found the ancient seat of House Harlaw, Harlaw Hall, too damp and flooded after three sons died in infancy.
Lady Alannys Greyjoy lives at Ten Towers with the current Lord Harlaw, her brother Rodrik.
- Ten Towers at A Wiki of Ice and Fire (spoilers from the books)