It takes about half an hour with the District Line from London to Richmond.
From the Station you can walk to the beautiful park.
The park is a nature reserve, you can find many free running deer.
I recommend packing a backpack with a picnic blanket and enough food, because the food supply in the park is rather sparse, next to a small coffee stand you will find nothing more than pure nature.
Don’t worry, the deer are usually peaceful. However, caution is required if you take a dog with you; at certain times of the year, deer do not react very friendly to our four-legged friends.