Three YMCAs:
#1) This is the one next to the Peninsula.
http://www.ymcahk.org.hk/sales/html/hst001e.htm
Here is a map of TST (copied... I am afraid, from the MTR website). The YMCA is #30 on the map.
#2) This is the one in Yao Ma Te
http://www.intlhouse.ymca.org.hk/
#3) this is the one on Harbour Road (Wanchai, Hong Kong)