Guess what this is!
A temple?
Not exactly.
It’s a well near a temple in Kanchipuram, commonly called ‘Nadavaavi Well'. Well, it’s not just a well, there’s a small underground cellar inside the well. In the above picture you are looking at the entrance of the well, with steps leading downwards.
These are the steps of the well which lead to the underground cellar. During rainy season, the whole cellar gets submerged in water and water comes even up to the top of the stairs.
During the summer, the water level decreases and underground cellar is visible.
This is the underground cellar. How beautiful it is. The cellar is a twelve pillar structure. The pillars are very awesome, intricately detailed and have very precise corners. In the middle of the pillars, the well goes deeper. You'll find water inside it.
There is ample space surrounding the pillars where people can move freely.
Now, let's go to the core part of answer.
The Varadharaja Perumal of Kanchipuram visits this well on every Chitra Pournami. The vigraha of Varadharaja is brought to the Nadavaavi well.
The water inside the mandapam is drained out on that day. Lord Varadharaja comes inside the well, stays there for a while and then moves out. A large number of people visit the well to witness this beautiful ritual.
The above picture shows Varadharaja inside the well cellar.
After the ritual ends, the water slowly fills the mandapam and it gets submerged inside water. It will be an awesome sight to see.