One can definately check out Wong Tai Sin Temple, easily accessible by the MTR (Kwun Tong Line) and is situated by the station that bears that name. Or head out to Sai Kung and explore the fishing village there.
I could also suggest heading out to the Gold Coast (no I am not talking about Australia as HK has one named with such) near Tuen Mun, but with the OP being from Europe, not sure if Mediterranean style type of beaches and scenes will be appealing.