The park is perfect for bird lovers, if you're patient enough you'll see many colorful birds some species only found in the Philippines, such as the Tarictic Hornbill. You might also spot eagles and monkeys. There's also a nice waterfall nearby you can swim in but it's only accessible by boat.
The trekking required is minimal. It takes about 5 minutes to walk down to the first lake, then you can either walk about 1 km to the second lake or hire a paddle boat to take you there (you'll still have to walk a bit). There's an observation tower in between the two lakes. The view from up there is amazing, it's also a good spot to see birds.
There's a good and affordable restaurant inside the park with a nice view of one of the lake. Perfect for lunch.
How to get to Balinsasayao Twin Lakes:
The best way to get there is to rent a motorbike, you can also go to the waterfalls in Valencia on the same day. You'll find scooters for rent for 400 pesos in Dumaguete, prefer a semi-automatic as the roads are pretty steep. The view from the road is just amazing, you'll see the whole bay.
Another option is to take a jeepney or bus along the main road and ask to be dropped off at the intersection and then take a habal-habal up. There are plenty of them waiting just for that.
For the more adventurous type, you can also undertake the 15km trek from San Jose to the Balinsasayao Twin Lakes. You'll find several waterfalls on the way as well as a couple of Bukidmon villages (local tribe inhabiting the area). You might want to hire a guide as there's no marked path.
Lake Balinsasayao entrance fee:
The entrance fee is 100 pesos for foreigners and 50 pesos for locals.
Other things to do in Dumaguete:
On the same day, you can go to Valencia. There, you can go to a waterfall, take a dip in a hot spring and visit the WWII Museum.
You can also visit the Manjuyod sandbar in Bais and go dolphins watching.