The Coimbatore airport is the closest to the hills at 3-1/2 hours by road. There are flights into Coimbatore from Singapore, Sharjah, Colombo and most parts of India including Mumbai (Kingfisher, Indian Airlines,Jet and Go Air), Chennai (Spicejet, Air India, Indigo and Jet) and Bangalore. The Mysoreairport is about 4 hours away from Ooty by road but There are no scheduled air services to anywhere from Mysore Airport since quite a while. Also Kingfisher has ceased operations since acouple of years. The road trip is quite scenic from either airport.
The hills are connected to by a nightly train. The Nilgiri Express (Train No. 12671) leaves from Chennai at night, and reaches Mettupalayam (which Indian Railway spells as Metupalaiyam), a small town at the foothills of the Nilgiris early the next morning. The train The Nilgiri Mountain Railway leaves Mettupalayam at 7.10 pushed by a small steam powered historic locomotive that is a remnant of Swiss engineered trains imported in the late 1800s. The train journey will be a very good experience, but only 30 tickets are issued on the spot. A separate queue for this train is at Mettupalayam railway station. You have to be in queue atleast by 5 am. A token will be given from there and you have to take this token to ticket counter(outside the platform,yellow building),get the tickets and get back to the same queue. If you are a team, one can represent for taking token and tickets but all have to be present in queue while embarking the train. Try to get a seat to farther side of platform as this side offers maximum viewing experience. The steam train is much smaller, and can only accommodate a portion of the passengers that disembark at Mettupalayam.You have to book separate ticket for this journey (tickets can be booked through IRCTC(www.irctc.co.in) like any other rail ticket booking.), although many prefer the faster route of taking a cab or a bus from Mettupalayam.
There are buses and shared taxi vans that can be boarded from Coimbatore to Ooty. If you don't want wake up early to take the train from Coimbatore, plenty of buses are also going to Ooty.Also there are plenty of buses leaving from Bangalore and Mysore for Ooty. The Coimbatore "new bus station" has frequent bus service to Ooty via Mettupalayam, and it takes around 3-1/2 hours to get there. On the way back in morning, some busses make a 10-15 minute stop over at Mettupalayam for breakfast. From the "new bus station" it takes about 25minutes by (another) bus to reach the Coimbatore railway station. From Kozhikode (Calicut) there are two government buses daily, leaving 05.00 and 07.00, travel time is about 6 hours. Mysore is served few times a day, too. From Kannur there is a KSRTC Bus starting at 7.30 am everyday and a Tamil Nadu Bus at 10PM everyday reaching ooty at 4PM and 7am next day respectively.
The Nilgiris are in Tamil Nadu, but it is quite near the borders of neighbouring states Karnataka and Kerala. The hills consequently can be reached from within Tamil Nadu by travelling up a heavily forested winding road, with many sharp hair-pin beds. The road trip from any state is quite scenic, although the Coimbatore-Mettupalayam-Coonoor-Ooty road (i.e. the Tamil Nadu route) is the most travelled and well maintained. All roads to the Nilgiri hills are toll roads, although the tolls are quite nominal. If you are planning to visit Ooty and Coonoor from Bangalore then the road trip from Bangalore is the best option to enjoy the scenic beauty & opportunity to click lovely pictures of mountain peaks & tea-coffee plantations. One can travel by booking a taxi from rental service providers.