Tycho continued with his detailed observations, often assisted by his first assistant and student, his younger sister Sophie Brahe. In 1574, Tycho published the observations made in 1572 from his first observatory at Herrevad Abbey. He then started lecturing on astronomy, but gave it up and left Denmark in spring 1575 to tour abroad. He first visited William IV, Landgrave of Hesse-Kassel's observatory at Kassel, then went on to Frankfurt, Basel, and Venice, where he acted as an agent for the Danish king, contacting artisans and craftsmen whom the king wanted to work on his new palace at Elsinore. Upon his return, the King wished to repay Tycho's service by offering him a position worthy of his family; he offered him a choice of lordships of militarily and economically important estates, such as the castles of Hammershus or Helsingborg. But Tycho was reluctant to take up a position as a lord of the realm, preferring to focus on his science. He wrote to his friend Johannes Pratensis, "I did not want to take possession of any of the castles our benevolent king so graciously offered me. I am displeased with society here, customary forms and the whole rubbish". Tycho secretly began to plan to move to Basel, wishing to participate in the burgeoning academic and scientific life there. But the King heard of Tycho's plans, and desiring to keep the distinguished scientist, he offered Tycho the island of Hven in Øresund and funding to set up an observatory.