The tower to the left was the main sanctum sanctorum containing the deity of Sri Madan Mohan that had been constructed under the orders of Maharaj Vajranabh, the great grandson of Sri Krishna (Madan Mohan).
The original deity was hidden by the brahmins when Mahmud of Ghazni rampaged the area near 1000 AD, to be rediscovered by Sanatana Goswami in early 16th century.
This temple was constructed by a salt merchant with the blessings of Sanatana Goswami. However, Mughal emperor Aurangzeb, who could see the great opulence of the newly constructed temples of Mathura-Vrindavan from his capital Agra, became envious and ordered all the high temples to be humbled, so that none could match the greatness of Mughal architecture.
The Madan Mohan temple was desecrated by the Mughal army, but Sri Madan Mohan was taken into the protection of Rajput kings. The original deity can still be visited in Karauli, Rajasthan. In Vrindavan, the replica of Sri Madan Mohan is worshipped in humble way.