He doesn't actually give her a specific geographical location, but uses the phrase "nunnery" as a metaphorical way of telling her to:
* Leave the world and its troubles: Nuns were expected to live a life of seclusion and devotion, away from the dangers and complexities of everyday life.
* Reject men and the possibility of love: Hamlet is disillusioned with women and suspects Ophelia is part of a plot against him. He believes that men are corrupt and women are easily manipulated.
* Find a safe and pure place: He implies that the world is a dangerous and corrupt place, and a nunnery is a place where she could be safe and protected.
It's important to note that this is a complex and ambiguous moment in the play. Hamlet's words could be interpreted in several ways, and his true motives are unclear. He is clearly suffering, both mentally and emotionally, and his words to Ophelia may be motivated by his own pain and confusion.