It depends @Amy3 India is a land rich of culture and heritage and it is very very diverse – probably the most diverse of countries that you will find on this earth. I have spent my entire lifetime here and haven't been able to see Everything.I still have lots and lots to explore.I live in the Northern Part and there is too much to see.
You can start with the princely state of Rajasthan and enjoy the forts and palaces,safaris,deserts.lakes,the people and the food.If you like hills and valleys there is always the beautiful Himachal Pradesh and SHIMLA in particular.From a historical perspective you cannot miss Tajmahal in Agra,one of the wonders of the world,a mere 3.5 hour drive away from Delhi.
Beach Lovers can go to Goa and Kerala with the most pristine beaches and enjoy the local delicacies too.For the religious minds and those who seek solace for their sins can go to Varanasi in Uttar Pradesh,Haridwar and witness the puja of 'Ganges' the Holy River.If you just want to chill and relax and have fun,you can always go to Mumbai-The city that never sleeps.
There are many many more places to visit.One Place or One Week is not enough.It's just an overview but one thing is for sure that your journey will be incredible !!