Bastrup Tower, also called Bastrup Ruin is a medieval ruin located approximately 50 meters north of Bastrup Lake at Lynge in Allerød Municipality. Since the source material about the tower is very sparse, not much is known about the builder, but it is believed that the tower was built in the first half of the 12th century by Ebbe Skjalmsen, also called Ebbe de Bastetorp, an uncle of Bishop Absalon. With its 6 meter thick walls, built of ashlar, and an external diameter of 21 meters, the structure was among the largest in Northern Europe at that time.
https://www.kulturarv.dk/fundogfortidsminder/Lokalitet/93841/
https://tidsskrift.dk/historisktidsskrift/article/view/50620