Much of the Los Cabos coast is too rough to swim. These three beaches are the exceptions: two quiet snorkelling bays on the Corridor and the busy town beach.
Along the 30 km Corridor between the two towns, big swells and steep shelves make most beaches dangerous. Check the flags, and choose the beaches that are known to be safe.
Playa Chileno is a wide, sheltered bay with lifeguards, shade palapas and good snorkelling off the rocks at its eastern end. Neighbouring Bahía Santa María is a horseshoe cove protected from the swell, with a reef along both arms where you may see tropical fish and the odd turtle.
Both are best in the morning, before the afternoon wind picks up.
Playa El Médano, in Cabo San Lucas itself, is the town beach: a long curve of sand facing the arch, with beach clubs, jet skis, and the water taxis that run to Land's End.
Snorkel in the morning, finish on Médano.
Walk down from the car park and snorkel the reef while the water is still.
Move to Chileno for more snorkelling and a swim near the lifeguards.
Drive or take the bus back along the Corridor to Cabo San Lucas.
Find a lounger on Médano, with a view of the arch.
If you have time, take a boat out to the arch from the sand.

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Chileno and Santa María have signposted car parks on the Corridor highway; local buses stop nearby.
Chileno has toilets and shade; Santa María is simpler; Médano has everything.
Photographs from Wikimedia Commons and Pexels under their licences.