Eric Satie's Gymnopedie Nr. 1 is a beautiful and tranquil piece for piano solo. Here you can get free sheet music and helpful tips on how to learn it.
Others are timeless and beautiful like the "Gymnopedies" and the "Gnossiennes".
One of the most well known pieces for piano is the first of the 3 "Gymnopedies", that you can sometimes hear as background music in movies.
The piece is great for an intermediate level student.
It is relatively easy since it is so slow, but there are some technical challenges in how to keep the melody flowing and balanced above the repetitive accompaniment.
The change of the accompaniment from one hand to the other also needs to be smooth and balanced.
Let's start by watching the piece being played: