You can travel to Lucknow, Rajgir or Allahabad if you want to explore within Uttar Pradesh. Or Bodh Gaya in Bihar (6 hrs drive) and Khajuraho in MP (9hrs drive) are some other interesting options.
Day 1: Go on a boat ride, you'll get to know about all the ghats of varanasi.
Day 2: Visit Kashi Vishwanath Temple, Annapurna Temple and Kaal Bhairav Temple. Time To visit this place depends on the crowd.
Day 3: Visit New Kashi Vishwanath Temple, Tulsi Manas Temple, Sankat Mochan Temple, Durga Temple and Tridev Temple. This would take 2-3 hours. If you have time you can head towards sarnath where you can visit Sarnath Temple, Tibetan Temple, Chinese Temple, Japanese Temple and Sarangnath Temple