Go to the night safari
Pack a picnic or a bbq for 2 and fish at the same time.
The museum has some pretty interesting exhibits now. No longer like in the past
Every Friday (can't remember the time) the Art Museum offers free entry

Try to appreciate classical music, just go to the SSO once for the experience of it
Taking a walk in the zoo or bird park can be pretty fun too.
Learn something new together. Be it dancing, skating, sewing teddy bears, jewellery etc
Make something together eg. build a miniature fountain. Very simply. Need a deep bowl or whatever, the items you wanna use to raise things up or whatever cute items you wanna stick on it and a fish tank pump. Remember to use clear silicon glue.