No special access issues
There are many parking options in Olympos. You can park by the road or park by the Ancient city, the parking is 10 liras. The access is from 3-15 minutes, it depends where you park/stay. For some of the sectors you will need to cross the river, it water level changes with season, but it is usually not a problem.
The sectors which are by the beach are accessible if you pay the entrance fee for the Ancient city (40 liras), it is free to enter after 17 o´clock. It takes about 25 minutes walk to La Plaj from the parking and 20 minutes to Cennet. To get to the Ceneviz Liman and Mağara sectors you will need a boat, total access time from parking is about 30 minutes. Renting is possible with Kadir´s Tree Houses. There are fixed ropes so you can get to the sectors.