I visited this area in December 2016.
This is usually the main region of rainforest that birdwatchers go to get the avian Sri Lankan endemics. However, I found the area to be overrated and rather limited in activities. You are only allowed to explore the national park with an escort, and some of the staff here can be very aggressive, creating an unpleasant atmosphere. The lodges here such as Martins and Blue Magpie don't seem to be fulfilling their potential anymore. I found the rainforest alternative of Kithulgala to offer a much nicer experience.
Even though Sinharaja is not physically far away from many of the southern cities and national parks, because of it's hilly terrain and small roads, it takes many hours to get here.
There are as usual many accommodations around, but the only options for keen naturalists are really the three that are very close to the park gate in the village of Kudawa; the Blue Magpie, the Sinharaja Birder's Lodge, and Martins Lodge.
The Blue Magpie is located on Pethiyakanda Road leading to the Sinharaja Reserve. It is about a 10 minute walk (1 kilometre) from the ticket counter at the entrance. There is a lot of construction both in the hotel and surroundings. There is a food table for birds, but if there was once Blue Magpies attracted there, they have probably been scared off.
Martin Lodge is a bit trickier to find and get to. Indeed, it is hard to book, and there are no signs pointing to it. Once you have crossed the final river and turn left to go to the national park entrance, there is small road going to the right and up to the ridge. Follow this bumpy road through the tea plantations and forest for about a kilometre or two. It is just before the road ends and splits into the national park. Just be aware, that if you stay here, even though you are closer to the park than at the Blue Magpie, it is harder to get into the park. If you want to enter the national park, you will have to go all the way back down to the entrance on the main road. This is a real pain for birders who want to get up early. I also checked out Martins in the morning and late afternoon, and I didn't see a single bird come to the feeders!
Unfortunately the lodges here don't seem to be fulfilling their potential anymore, with lots of noisy construction and clearing going on, and a lack of the more interesting birds coming to the feeding tables. However, the hotel staff are pleasant, and the hotels make good bases. Don't expect information to be offered; you have to ask questions to find out information about walks in the area, etc.
There are several walks that can be done in the area. Walks can combine some rainforest, rivers, and more open villages.
If you staying at the Blue Magpie, the walk up to Martins is quite nice, and goes through some forest.
Another walk from the Blue Magpie follows a river up a valley. From the same main road, take another similar small road on the right (as with Martins), but this is the one before (opposite Sinharaja's Bird Lodge). Follow the small road for a kilometre and you will hear the rushing river. There are various tracks through the forest that go down to the water.
You can walk from the village .
On these walks you can usually see dragons and birds. Earlier in the morning is better to see Blue Magpies.