Staying in St Lucia for a week in July 2016 gave me gave me ample time for visiting the Pitons Management Area. I would recommend a boat excursion for a great view of the hills, and the bonus of being able to enjoy the reef and aquatic life that are included in the WHS inscription. Being an "inveterate WHS collector" this wasn't enough, though, so I also organised a guided ascent of Gros Piton.
There is no real climbing required on the ascent of this, the larger of the two hills, but it was a steep walk all the way up. Fortunately the route is entirely shaded from the sun by tree canopy so we didn’t have to worry about sunburn. There is a great viewpoint about halfway up from which we got a different angle on Petit Piton.
The view from the top is not as good as the one halfway up because it looks out onto the relatively flat southern end of Saint Lucia. Still, you definitely get a sense of achievement as you appreciate how far you have climbed.
A large rock-mounted WHS logo is one of the better ones I’ve come across on my travels. It stands on the roadside on Petit Piton, overlooking Gros Piton.