She does bring a bag with two books in case they find somewhere to sit and read, and then off they go!
There's a large open green space around the castle itself, including down to the lake on the other side from the train station - which seems to be a popular hang out spot. The Quidditch Pitch is on a flatter area overlooking the lake. But there's also a really big, dark forest sort of folded into a much smaller bit of land inside the sweeping walls (with 'Dangerous - Keep Out' signs in a perimeter around it), and smaller, lighter patches of trees and hedges and bushes, and stacked stone walls and cottages and outbuildings - one of the cottages down near the Forbidden Forest is occupied, but a lot seem to have been unused for a really long time.
There's extensive gardens and greenhouses around the Herbology classroom (and a cottage by there as well, which has been transformed into a classroom for less hands-on lectures). There's a few meditation mazes tucked away here or there, and some flat areas with signs they've been used for rituals in the past.
You could fit a village or even a small medieval city inside the walls easily, and there's signs there used to be inner sets of walls at some past point.
Some of the gardens and cottages have paper signs fixed to the entryway with some variant on 'claimed by this or those students' and then years. Lots of the claims seem to have expired, and lots are unclaimed.