Any of the southern coastal walks will be very nice tomorrow, like La Perouse, Kurnell and Royal National Park and you might even see some whales - but only the Royal National Park ones would have train access, you’d need a bus or car to the others. I think it’s still a bit of a walk from Otford to the track, and then it’s another 2 hours one-way to get to Era beach or so. What about going to Watsons Bay, or heritage walk in Vaucluse, presumably you can go to Edgecliff station? Another very good one starts from Mt Kuringai Station to Berowra station on the Benowie track (enter from Glenview Road) - very peaceful as not as well known as the southern ones.

Awesome experience! They have been pretty active although a bit far out from the coast, need binocs but have seen them on the Kurnell/Captain Cook and La Perouse trails.