From Marla you can reach the town Cilaos in the heart of Reunion via the Col du Taïbit (2081 m). The reward for the steep ascents (you should have a head for heights) are great views of the distance between La Nouvelle and Marla.
Once you have mastered the ascent to the Col du Taïbit, you can see two mighty calderas - the Cirque de Cilaos on one side and the Cirque de Mafate on the other.
Then from the Col du Taïbit it's mostly downhill to Cilaos, a town in the heart of Reunion.
(NB This hike is very beautiful and you should be in good physical condition to enjoy it)