Hi Linda,
The Botanical are nice and for an afternoon outing, they have birds, a few animals and nice
flora in a park setting. Also Adventure Park is even better and has some amusements. There is a museum. Vision City Mall is safe and has shopping, cafes, coffee shops, food court and a nice Cinema showing current movies. Connecting with folks who have been in PNG for a while will allow you to experience some of the city you won't normally see on your own. They can also take you a village to experience PNG life on a local level.
If you are here for the 40th Anniversary of PNG Independence in the middle of Sept there will be a lot of cultural shows that will be awesome.
My wife and I would be glad to show you and your husband around some if you are interested in getting out for more than grocery shopping. Please reply to me via email or message and we can connect when you get into the country.