Ba Ho waterfalls, Near Ba Ho village (Approximately 20Kms North of Nha Trang - cross the bridge closest to the sea and stick to it for the safest and most scenic route). A series of three waterfalls and a quite fast flowing at (some points) river tucked away in the forest. Its a good one hour trip from Nha trang by moterbike through some rougher rural road tracks ( especially in the wet season ) If you get a flat tire it can be fixed by the locals for a small fee.
The turn off from the main highway north of Nha Trang is hard to miss (there is now a blue Ba Ho sign and arrow). Most locals along the road should be able to point it out. from the turn off its a straight track to follow to the river, there are limited amenities there although you can buy food, like rice and chicken and cold beers or soft drinks are also for sale from locals who will guide ( Follow ) you up through the forest this is preferable to having to carry your own food and drink and the prices are reasonable a small premium for their trouble, the "guides " are pleasant enough showing you short cuts and footholds higher up the track.
Taxis and motorbike guides are available in Nha Trang to take you there but its not too difficult to find yourself and in better weather, a pleasant drive, if you're confident on a motorbike. be warned though that going off road on hired bikes can incur damage which you will be liable for.