If you can walk a mile or so on compressed sand, it's really worth walking out to the tidal flats at the sanctuary. They run many tours with a naturalist (highly recommended) who will point out lots of interesting things along the way. Each naturalist will point out different things, which is why I never find this walk old.
Often is you go on the "Seashore Scramble" or a similar walk, the group will bring out dip nets and a big seine net. This is so much fun is you like discovering what nature has to share and don't mind getting a little wet or dirty.
This is always on my must-do list every summer!