Maria Keil was a Portuguese artist, whose most visible works are seen by millions every day although most people don't glance at it twice: from the 1950s to the 1970s she did the original tile decorations for Lisbon's underground network, except for one station, where it still stands today (*). With this work, she helps modernise a traditional art form in Portugal, reinventing it to the 20th Century - something so many others continue to do to this day. She wasn't allowed to use any figures as that was seen as distracting. So she used geometric/abstract patterns.
She also did a lot of more traditional graphic work, particularly book covers and illustrations. The photos below were taken by yours truly - if I had more talent and material adjusted to take photos inside underground stations they would have out come much better. Alas, it should give some idea.
(*) In two stations (Saldanha and São Sebastião) the original tiles got removed for some reason, and in Restauradores, some of it was also lost during renovation works. Everything else is still there, and the new decoration in São Sebastião is also hers (last photo). It seems it was her last work.