Yelagiri hills is concentration of many villages. Our first visit was to the Nilavoor lake. To say it as lake is an exaggeration, it is nothing but a pond with not so clean water. Surprisingly, few people were boating. It just departed from this place. It is best to avoid this pond.
The next place we visited was Murugan Temple on a hillock. I did spot many birds near that place.
We then went to the main lake, Punganoor lake in Athvanoor. The lake is reasonably big surrounded by hills. We had a panoramic view of the lake from a watch tower built on a tree. Some time was spent on boating in this lake.
We had planned to trek to SwamiMalai, which is the highest point in Yelagiri. We had our early lunch at Surabhi Hotel a small restaurant. The “big” hotels had a very long waiting period for lunch as they had not prepared anything!!
The trek to SwamiMalai starts from a village Mangalam. The trail was quite simple and defined. We were not in a hurry and did climbed at leisurely pace. One hour of climb took us to the top. There is a small Temple and a wireless receiver at the top. The view of Yelagiri valley can be seen from this place. We spent some time idling around. The descent was even more easier and by 4PM we were at Mangalam village. It was then time for return back. 
On the way back, we decided to visit Krishnagiri Dam, near Krishnagiri town. Surprisingly, it turned out to be a good spot. The Dam was quite huge and there were nice garden in front of the Dam. I was bit surprised that being so near to Krishnagiri and on a Sunday evening, there were hardly any visitors. 
Route to Krishnagiri Dam:
From Krishnagiri, go towards Dharmapuri. After 5 kms there is an arch on the right side. Take that road and Krishnagiri Dam is 2 kms from that Arch.
We had our light snacks at Annapoorna Hotel at Krishnagiri and started our journey towards Bengaluru. This journey was slow because of the traffic all along the route.
More Information:
Yelagiri Hills is in Eastern ghat, so do not expect the place to be very cool. The forests are also dry deciduous unlike the evergreen ones we see in Western Ghats. This place is not yet commercialized and is a nice place for people who would like to have a relaxing day without much activities. More picture of this trip can be seen here.
Selvam
Seems Idle spot for One day trip from Bangalore or Chennai.