Great view of the lake and worthwhile excursion destination. The tower belongs to the "Schaalseehof", which offers a hay hostel and fish smokehouse in addition to a courtyard cafe. More information at: schaalseehof.de
No, there are not many lake accesses on the island. This is probably because the lake is under protection. Here is such an approach, but the hard-to-buy: It goes crunchy …