Choose a small first day
Start in Cascais town with a walk through the centre and along the waterfront. Keep lunch and your return journey close enough that a missed connection does not spoil the day. A walk on a map can feel very different with wet beach equipment, strong wind or a tired child; leave space between the things you want to do.
Check the railway before leaving
The Cascais railway connects the Lisbon waterfront corridor with Cascais and includes Carcavelos and Oeiras. Check CP for the actual service on your travel date, including engineering work and replacement buses. Do not build your day around an old timetable screenshot. When booking a lesson, ask the school which meeting point is practical from your arrival station.
Treat Guincho as a separate outing
A visit to Guincho needs its own plan for the journey from town and back. Allow for exposed weather and confirm transport before walking away from a stop. If the connection makes the day feel rushed, save the beach for another day and enjoy the town coast instead.
Pack for the return trip
Bring a dry layer, drinking water and a bag for wet clothing. A change of plan is easier when you are comfortable. Save the return route before setting out and agree a meeting place if your group splits between a beach, a lesson and a café.