You can start your day by waking up early in the morning so that you can start your journey towards Mathura. Check out from the hotel and start your journey. Mathura is only 3 hours away from Delhi. You can go there either by train or by car.
After reaching Mathura you can check in and have your breakfast. Then you can go sightseeing at the famous temples and pilgrimage sites which are all dedicated to Lord Krishna. You can start your journey by first visiting Gokul. Some places you can visit in Gokul are Raman Reti, Chinta Haran Temple, and Brahamand Ghat. Then you can visit Mathura and some famous places in Mathura are Dwarkadheesh temple, Sri Krishna Janma Bhumi, Vishram Ghat, Gita Mandir, Radha Kund and many more.
Then you can visit Vrindavan and can visit the most famous temple there which is The Banke Bihari Temple.
This temple is mainly known by the devotees of lord Krishna. One of the oldest temples in Vrindavan is the Madan Mohan Temple and the most beautifully designed temple is Sri Radha Raman Mandir temple. There are also some other temples that you can visit if you are left with time, they are the Prem Mandir, ISKCON temple, Vrindavan Chandrodaya Mandir and more. You can return to the hotel and have dinner and stay overnight in Mathura.