The Aquarium of Western Australia opened in 1988 under a different name. It features the largest underwater tunnel in Australia (Wikipedia) and a touch pool, where anyone who can reach in has the chance to feel a stingray, fish, starfish, or anything close enough. So, yes, I was back in Perth again and made a morning of it.
touch pool 
outdoor touch pool
indoor/outdoor cafe 
outdoor messy play
The cost of entry was quite high for adults ($30) and possibly making it a once-off event for me. I would definitely recommend it and had trouble picking out which photos to display. I also took a number of mini videos of jelly fish doing their thing, seahorses and many other underwater moments that I didn’t feel were captured by photos.
There is an old ship – the DUYFKEN, which I am not sure as to whether it is a recreation or restoration and you can take tours or just view it from the outdoor area. I believe diving and glass bottom boat rides are among the other activities offered at the AQWA.
The beach is nearby and there’s a large park out the front where you could have a picnic or run after the indoor event. The Aqwa is in Hillarys. We spent about 2 hours there and seemed to go very fast, as it was really visually beautiful and enjoyable.
Underdown 