If you enjoy walking you can leave your car and walk on the NT footpath to St. Just's beautiful church and garden and from there continue along the water's edge to St. Mawes. Once in St. Mawes there is a selection of boat trips ( from Easter onwards) which can take you across the Bay to Falmouth, up the Fal to Trelissick Gardens (NT) or on to Cornwall's cathedral city of Truro and many others to the various creeks and waterside inns etc.
You can drive (5mins) to Smugglers Cottage, have a coffee or lunch and pick up a boat there up river to Truro or down river to Falmouth with stops en route.
If you fancy a quiet day at home, there is beautiful Messack itself. Stroll along the drive and walk across the fields on the NT footpath and the view is breathtaking. You can even scramble down to the water's edge and if the tide is right, have a swim or a paddle!
The Roseland offers training for sailing, canoeing, kayaking, wind surfing and all the usual water sports. There is horse riding, tennis, squash courts and cricket on Saturday afternoons.
The King Harry Ferry is a 10 min drive and saves you many miles if you wish to explore the West of Cornwall. Penzance and the wonderful Penlee House Museum & gallery where there is a great collection of Newlyn School paintings, many galleries and more individual shops than Truro which has all the stores you find in every big town. Helston The Lizard Peninsula, St. Ives and not to be missed the Minack Theatre nestling into the clifftop at Porthcurno.