Thanks, Sean! Some background from Sean:
'Sutro Sam' is a river otter that has found his way to San Francisco (from where is unknown, but Marin has been suggested, meaning he would have swum the Golden Gate) and taken up residence in the brackish waters of the ruins of the Sutro Baths. Recently featured on the news, he has been the subject of great curiosity, attracting modest crowds; regardless, he has been out and building a nest in an old concrete drain, from which he pops out his head from time to time.
Edit: A couple of commenters remind us that dogs are temporarily not allowed in the area immediately surrounding the baths, so please plan accordingly if you'd like to visit Sutro Sam. More information in comments below.