Horse back riding
It's popular here. In one hour you can go around the lake or longer rides you can visit countryside around Ooty. Some knowledge of horses would be good as the guides are local men who don't speak too much english, teaching is minimal. On top of the price you have to pay for guide.
Most travel agents / hotels conduct guided tour packages that will bundle you into a bus, and tick off the most important and hence crowded "tourist" spots in the area. Some hotels also arrange for private cars like Indica, TATA Sumo.
Enjoy the weather.
Travel on the railway. The charming Nilgiri Mountain Railway NMR, blue and cream with wooden coaches and large windows, is widely regarded as a marvel of engineering.
Go for long walks and hikes.
Visit a tea plantation and if possible a tea factory.
Ooty is famous for its choclates, and the best place to have them is at King's Star. They have around 4 outlets in Ooty and are the first chocolate makers in ooty. the shops are run by the 3rd Generation of the family
Travel the country side in a 4x4.
Catch a round of golf at the Gymkhana Golf course membership or introduction required
Visit the local Army cantonment - the Madras Regimental Center and the DSSC Defense Services Staff College.
Visit terrace farmed cabbage fields around Ooty.
Visit the Mudumalai forest sanctuary 1-2 days minimum.
Visit the Needle industries which is around 6km from maintown Ooty in Ketti.
Visit 9th mile and also the 6th mile where lot of movies are shot:-)
Visit the Municipal Market and shop for fresh local fruits.
You can get farm fresh carrot on the way.