(S/E) From the start W3W>>> walk up onto the promenade and walk east. The option is to walk along the beach, near Marazion, where there is a footbridge over the Red River; Cornish rivers, like the Red River, are called "red" because of the mineral deposits and waste from centuries of tin and arsenic mining that stained the water, giving it a reddish-brown hue. Continue to the Causeway steps.
(1) Crossing the Causeway will always depend on the tide; if the tide is in and the intention is to visit the island, there is a boat ferry service. With the tide out, walk across the Causeway.
Option: pay the entry fee, and explore the island. (2) can be missed and proceed to (3).
(2) Walk back across the causeway, or catch the ferry; be mindful that the ferry service is seasonal. Look out for the memorial stone HMS Warspite to your left, then walk up through Marazion (Beacon Road). Heading up through the narrow streets, turn left up Rosehill. As the lane levels out, a lane on the left will be met.
(3) Turn left down Green Lane, heading initially north, then south at the bottom of the hill. The bird sanctuary is on the right, through the gate.
(4) Option to enter into the sanctuary, please consider any bird watchers, as they like a silent approach. Or continue on and cross the main road. Rejoin the promenade heading west to the start (S/E).