The section of Kusu Island facing the open sea has very strong waves, so be very careful and do not swim here. If you want to swim, do it in the lagoon area at the calm side of the island. The water here is calimer and meant for swimming.
In order to visit the hilltop Kramats (holy shrines of Malay saints) of Kusu Island, you have to walk up a flight of stairs to the top of the small hill. It is not very high up, and there is a rest stop along the way.
Each year during the ninth lunar month (which falls between Sep and Nov according to the Lunar Calendar), thousands of devotees flock to Kusu Island for their annual Kusu Pilgrimage.
Do take of the crowds when you are visiting during Kusu Island during this period, and be prepared to wait longer for the ferries.