Bhagsu, a village a little higher up from Dharamshala is a popular trekking spot with a beautiful waterfall in the centre of it, where you can go take a dip. But due to the influx of the crowd the place has started to get filthy, so please ensure you don’t create any waste when you go there.
Start a conversation with a local and ask them for some hidden waterfalls (there are plenty), and maybe head there to have an exclusive time. There is a famous temple right down the trail from the waterfall that many Shiva bhakts go to pray at.