The highest mountain of La Reunion is called Piton des Neiges (3069 m) which means snow mountain, since it is the only spot of the island where snow might exist during certain weather conditions. But usually, the summit is not snow covered and no special gear is needed to get on top of Piton des Neiges. However, the ascent is not easy at all since one usually starts in the Cirque de Cilaos or Cirque de Salazie at elevations of roughly 1000 m. Together with the Cirque de Mafate, these three giant canyons form to the south, north and west of Piton des Neiges.
You have several options to get to the top, however, all options usually include an overnight stay at Caverne Dufour, a mountain hut roughly 600 height meters below the summit. This is due to several reasons: first, for what I consider to be a normal hike, the elevation change from the Cirques to the summit (2000 m one way) is simply too large to do the whole hike in one day. It is certainly doable but you have to be in real good shape plus you won't enjoy the landscape on your rush up and down again. Second reason is the weather: the summit is usually in the clouds by noon. Best time to be on top is between 9 and 10 in the morning. At this time the probability for clouds is sufficiently low and the sun stands already high enough to fully shine into Cirque de Cilaos. Most people are eager to see the sunrise while standing on the summit, I personaly think that this is a waste of (sleeping)time. From my experience, a sunrise on top of Piton des Neiges is not at all different from a sunrise on any other place of the island, but maybe I'm just stupid. Besides, at 7:30 in the morning you don't really see anything but darkness in the Cirques. And believe me...you don't wanna spend two hours on the summit...it's freezing up there!

The most popular hikes to get to Caverne Dufour are to start 1) in Cilaos, 2) from Gite de Belouve or 3) in Hell Bourg. The first option is the shortest but also the steepest trail plus you can cut down the heightmeters to 1000 m if you take the bus to the parking lot Le Bloc. The hike from Gite de Belouve to Caverne Dufour is by far the easiest, since you are already at 1500 meters when you start. Still, it's a very long and steady up hill hike. The most strenous option is the one from Hell Bourg via Cap Anglais to Caverne Dufour since it is the longest plus you go the full elevation difference of 1500 m. First part from Hell Bourg to Cap Anglais (2150 m) is the worst...when you stand on the Cap you have basically done it. Also keep in mind that Hell Bourg is located in the Cirque de Salazie which is very wet so the chances for bad weather are fairly "good".
Once you are at Caverne Dufour the trail to the summit of Piton des Neiges is a two-hour hike (one way) over rocky ground. No special obstacles are on your way, it's actually a quite boring ascent. The view from the summit is ok but not spectacular. There are basically two things you can see: the Cirque de Cilaos just below and the Piton de la Fournaise in the distance. It is not like you have a 360 degree panorama of the island. On the way down to Caverne Dufour however, there is a small hill on the left hand side of the trail from which you have a great panorama of Cirque de Salazie, Piton de la Fournaise and Cirque de Cilaos. This hill is definitely worth a short stop.