We have booked a hotel in 88 Yee Wo Street, Causeway Bay, Hong Kong. We have a evening free.

Hi, the Causeway Bay itself is a famous shopping area in HK, so you can easily find the night market nearby. You can just walk there from your hotel.
For fun in the evening or at night, I suggest you go to Lan Kwai Fong, where there are many restaurants, bars and pubs of western style. You can enjoy yourself a lot there. It is only about 3km from where you are. So you walk take subway Island Line to Central, and then walk there or directly take a cab to reach there very fast.