The dry season from April to October is the best time for a travel to the north. Better access at dry months. Usually, it's very hot at midday. Avoid the rainy season from December to March. Tropical storms can occur and it is even hotter.
The Ankarana Special Reserve has three entrances. The main entrance in the east close to Mahamasina. From here you get to the most visited cave: Grotte des Chauve-Souris (bat cave). These two different caves are close together; to the right, you get to the flying foxes and to the left to the bats. This cave is much deeper with stalactite and stalagmites. We spotted several troglobites (reptiles or insects that live entirely in a dark cave).
There is one cave in the south of the National Park close to Antsaravibe and worth the effort to visit. It is the only cave in the world with cave-dwelling crocodiles. They can grow up to 6 meters.
More far away is the entrance to the west part the Ankarana N.P. A guided tour with 4x4 is necessary. At the western side are three caves located. It's possible to walk through all of them in a circular trail and they are not much explored. It is feasible to go there from the east and back in one day. Unfortunately, we didn't know that before and we had a lazy guide. Insist on it! It'll be a long day but can be done.
Important are a torch and a head light!