Complex sentence: Thiess claimed that three times a year, on the nights of St. Lucia's Day, Pentecost and St. John's Day, the werewolves transformed into wolves, and travelled to a place that was located "beyond the sea".
Split into simpler sentences: Thiess claimed that three times a year, on the nights of St. Lucia's Day, Pentecost and St. John's Day, the werewolves transformed from their human forms into wolves. This done, Thiess related that the wolves travelled to a place that was located "beyond the sea".