Today at Walden Pond

The pond is over 100 feet deep at it's deepest point.
For over a century admirers of Thoreau have added a stone to this pile as an ancient tradition to the lasting greatness of Thoreau's work.
These stones mark where the cabin that Thoreau built and lived in for two years and two months.

Henry David Thoreau wrote many books, "Walden" aka "Life in the Woods" is one of the best known non-fiction books written by an American.