Simon Ayres
Google
Very well presented and quiet place to spend a couple of hours.
I was lucky enough to get a lift from Port Grimaud to St. Tropez on a friend's Sunseeker, but there is a green ferry which makes travelling from St. Maxime or Port Grimaud easy.
The Citadel is well kept, and there is a lot to see. From old(ish) history to modern exhibitions there is plenty to take in.
The steps leading up to the Citadel look harder than they actually are, just take your time and you'll be rewarded with an amazing view before you know it.
Close to the main town, it's easy to get to.
From memory, entry was €5, which was a great price for the visit and the ticket office staff were very friendly.