No wonder you neck is sore you spin it around so dam quick haha.
Rottnest ferry is cheaper if you catch it from Fremantle than Hillarys, Still its a rip off.
On Rotto, a good close beach to walk to is "The Basin" is good for a snorkel and a swim and a perv, think you can hire snorkel stuff at the Bike hire place off memory (before you walk there). Its about a ten minute walk from where you will land on the Ferry. For such a close place its worth a snorkel there is some amazing fish life out there so close to the shore.
The pub near where the ferry lands does good food and atmosphere looking over the bay, Lamb cutlets ftw. Bakery does good pies, exy tho.
if you get stuck ask people at the shops they will tell you where to go.
If your into this sort of thing there is old artillery posts and the tunnels the guys used, and rail way lines they had to push the ammo along to each gun, the look out posts and shelters for the guns.
They were put on the island from WW2, it was there to protect Perth if boats came over. You can go on tours ect, i think the old people in yellow shirts take you, be careful or they will talk you ear off.
Me and my mates have gone to the areas that the tours don't take you where its just bush and no track and had a beer up there at night for the Aussie soldiers, its pretty awesome. Crawled through the tunnels ect lol.
My mate used to work on Rotto so we used to tear the place apart lol. A lot of fun to be had.