Ganz Basel posted a piece about the Nomad Hotel that openned in Basel in January 2016. In the last paragraph of the article, they mentioned that on the first night of Art Basel, Keanu Reeves sat next to them as he enjoyed his drink. The article is in German and included a HQ photo that has Keanu in the background. The original is posted below along with a cropped and enlarged photo focusing on Keanu.
Note: Keanu was in Basel for the the UN Aids Gala on June 13 that was held as part of Art Base.