hong kong is a bunch of coastal mountainous islands and the relatively flat peninsula of kowloon. central is fairly flat, as is kowloon. however, the north of hk island is separated by the south by mountains, just as kowloon is separated from much of hte new territories by mountains.
as such, there are some flat areas for walking, but even those are interrupted by streets, stairs, roads and more.
you haven't provided any necessary information (except that hubby will be working in central)....
we need to know:
(1) budget
(2) commute times you/he is willing to put up with
(3) what you like to do (other than walk in a park)
(4) size?
(5) ammenities?
(6) are you looking for a long-term service apartment/flat or are you looking for something for a month or two until you find a regular flat?