Solo Travelers can go anywhere it's not a big deal in the digital world lots of things are sorted and readymade on the internet
Still if you r new then You can Go 1. Rishikesh (Uttarakhand)
2. Gujarat (Statue of Unity and all)
3. Konkan (Maharashtra)
4. Leh/Ladakh
5. Manali/Shimla etc.
lots of there but you can try this one first.