Rottnest Island is super easily accessible from Perth, the ferry runs daily and a return ticket is about $80ish. It’s a really great little getaway from Perth and only a short distance. The island is 19 km² and there are no cars on it so you hire bicycles (or bring your own) and cycle around!
There is a camping ground on the Island and other accommodation options but they can get quite pricey if you don’t book in advance. We have been twice, once for the weekend and once for the day. A day trip is probably long enough. It takes about 2hrs to ride around the Island, pending stops along the way. You can see most of what there is to see in a day.There are no cars on the Island but buses do the lap around it if you’d rather hop on and off a bus instead of ride.
The water is super clear and we found some awesome snorkelling just off one of the beaches. So picturesque! There are a few surf spots around the Island and the native quokkas are soo cute! Happy little critters.