Theppakadu reserve forest is part of the Mudhumalai hills in Tamil Nadu and it is just across the border from Karnataka. It is about 250 Kms from Bangalore, the route is Bangalore->Mysore (SH17), Mysore->Theppakadu (NH 212, Ooty road). The road from Bangalore to Mysore is a 4-lane highway but after Mysore it is a 2-lane road and many sections are not so great (as of Jan '08). The drive from Bangalore, including a short break for food, took us about 5 hours. There are buses from Mysore (aging, state run) up to Bandipur but I have no idea where to find timings etc.
We reached Mudhumalai mid-morning at about 11:30 AM and stopped at the main office to confirm our reservation at the log house. The log house is a short distance from the forest department office and it has three rooms and a dining room. In theory, two of those rooms can be reserved by calling either the Mudhumalai office or the main office at Ooty. The third room is permanently reserved for the IFS warden. The rate is Rs. 300 per night for the double room and Rs. 600 for the one with 4 beds. In practice, the rooms are let out only to foreign tourists and govt officials (Sekhar chitappa made arrangements for us).
There are a couple of other places to stay inside the park - Sylvan lodge and the dormitory. Both these are also run by the forest department and are more likely to be available to anyone. The dorm is really cheap 20 bucks a night!! You can call ahead to make reservations: Mudhumalai/Theppakadu office 0423-2526235 or the wildlife warden office (Ooty) 0423-2444098. Other than these the only places to stay are some pricey resorts on the highway just outside the park (Karnataka side of the border). Their prices run about 1800 rupees per person per night. But it includes food and may include jeep safari into the forest. There are a few places to stay on the road to Ooty - Jain Resorts. I also spotted some tourists staying at houses in Masinagudi (7 KM from Mudhumalai on the road to Ooty). Regardless of where you stay you can eat at the log house dining room. The cook there charges per meal.
After lunch we sat around staring at the trees and the nearby stream till 4 PM and then went on on the safari bus ride. The safari route is through a small section of the sanctuary and lasts about an hour. There are no guarantees of spotting animals but there is a good chance you will. The safari is not very good for photo ops. The ride is usually packed full and the driver is on a strict time schedule. On the second day two forest guards took us into the forest by jeep. This was arranged by Appa's friend Srinivasan, a retired IFS employee. They took us 40 KM into the forest to an area called Congress Mattam. This is a grassy mound with fantastic views of the surrounding hills. This area is not open to the general public, infact the forest dept. on the Tamil Nadu side does not allow people to walk/hike in the sanctuary. So we were pretty lucky to get this opportunity. The Nilgiri biosphere is home to several types of wild animals. We sighted many along the way - herds of elephant, spotted deer, sambar, bison, and langurs. We also saw a lone elephant grazing at very close distance. I think the lone ones are elephants that have become too old and are expelled from the herd. We had originally planned a hike into the forest with Ganapati - another of Appa's friends. But because this (January) is elephant migration season we were advised against hiking. So we spent the last day at the log house but still had a lot of fun photographing the immediately ssurrounding area.
The forest department does not allow people to walk/hike within the sanctuary. I think the main reason is to save people from themselves (getting lost or eaten by an animal). On the Karnataka side some of the resorts arrange for hikes into the forest but I think that is outside of the sanctuary. The other option is to go on treks organized by the Nilgiri Wildlife and Environment Association or the Nilgiris Trekking Association.