Casco Bay which surrounds Portland itself is a Commercial and Cruise Ship area with limited beaches. There is a bikepath/walkway that surrounds the Portland waterfront from the bottom of Franklin St to the base of the Eastern Promenade. I have seen occasional sun bathers there but is is a bit rocky with no real privacy or wide open sandy beaches, lots of dogs though! If you travel about 7 miles south to Two Lights State Park you can view and climb on the rocky cliffs that are so very typical of the rugged Maine coastline. For sandy swim-able beaches you would need to go to Crescent Beach State Park about 8 miles southwest from Portland in Cape Elizabeth off of Rte #77. Also a great spot for dogs too as well as views of the fishing boats coming and going. Or you can go further southwest about 20 miles from Portland to Old Orchard Beach which is a virtual summer playground with miles of beaches, hotels, seasonal rentals, restaurant, small amusement and water slide park and all of the summer honky tonk you can imagine! Or if you head inland by about 35-40 miles you will find the Lakes Region with the second largest lake in Maine, Sebago Lake, along with a number of lake of all sizes. Also with lots of seasonal rentals, short and long term and local conveniences such as groceries, gas, restaurants and entertainment. Lots of water sports to enjoy in the Lakes Region too! Hope this helps? Where ever you choose to land, enjoy your days in Maine!