Sky Tower

Sky Tower is a tower in Solitude Hold near Katla's Farm, it's next to the carriage of Solitude.

Sky Tower is mainly a lookout, although in times of war, barricades are erected across the nearby road to act as a first line of defense.

Trivia
Despite being said to be a first line of defence, during the siege of Solitude it is not defended or already breached.

Source
Walking the World, vol XI

Appearances

 * The Elder Scrolls V: Skyrim