Complex sentence: Gammelholm was originally known as Bremerholm, or simply Holmen (Danish: The Islet), probably named for its pressence of merchants and ship builders from Bremen, and used to be an islet off Copenhagen in the strait between Copenhagen and Amager.
Split into simpler sentences: Gammelholm was originally known as Bremerholm, or simply Holmen (Danish: The Islet), probably named for the presence there of merchants and ship builders from Bremen. It used to be an islet in the strait between Copenhagen and Amager.