This is "A Bather" by Pierre-Auguste Renoir. Painted in the Italian north, Renoir's journey to Italy in 1881 rekindled his interest in depicting nudes and he began painting them far more often.
You can see that this small and intimate picture is probably one of a series made during the second half of the 1880s. Renoir added some recognisably contemporary touches, such as the striped fabric of the towel or the discarded dress that the model is sitting on, but by showing her seated on a rock by a pool or a stream, he was reflecting the longer tradition of classical nudes.
Note how Renoir sets the predominantly pink flesh tones against the greens of the background, which makes them appear all the more vibrant. The blurring effect of his brushwork suggests rather than precisely delineates the model and her surroundings, giving a sense of quiver or vibrancy that he sought to capture in this painting.
A Bather hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.