Next January we will spend an holiday in Australia.
We have only a day to spend in Perth.
We are undecided between a trip to the Pinnacles or a day to Rottnest Island.
Which are your suggestions ??
Thanks.

Depends what turns you on. I've been to both but would vote for Rottnest. You can combine it with some time in Fremantle, a cool place.

Just three weeks ago we were in Perth, and had time to do both. We felt that the Pinnicles were abit of a disappointment, we probably expected to much, or had already seen so many amazing things on our travels. But as for Rottnest Island, well, just go! It is such a beautiful place, excellent white sand beaches, crystal clear water, fantastic. We had arranged to go before leaving the uk, and after our first visit, we chose to go back two days later, to spend our last day in Australia on our 6 week honeymoon trip.
On our first day on the Island we saw 20 - 30 dolphins swimming off shore, playing in the surf, but we were unlucky as the previous day Whales had been spotted. On our second trip dolphins chased our ferry back right up until we docked in Freo. Before we went to Perth, we said 'We'll go this once, but never bother going back' but we fell in love with it, you'll have a good time.