Portland Maine's seaside location makes it a nice urban hub for a variety of day trips.

Just South of Portland in Cape Elizabeth there is the Two Lights State Park, which offers walking trails with spectacular rocky ledge views of the ocean.  Picnic tables allow for BYO lunches with outstanding views.  Low tide reveals tide pools and crashing surf.  Note, proper footwear is advisable.

Portland is also the gateway for the Casco Bay Islands.  The folks at Casco Bay Lines run daily trips out to Peaks Island and the other Casco Bay Islands. There is good hiking on Peaks and a couple of good restaurants.  There are also bike rentals available and Maine Island Kayak offers guided day and half day sea kayaking trips in the harbor and beyond.

 Just down the road is the Crescent Beach State Park, which offers a sandy beach and dunes, and is considered one of the nicest beaches around Portland.

Freeport offers outlet shopping twenty minutes north in a non-stripmall/non-shopping plaza environment.  Also, central to the town is the LL bean flagship store and factory store around which the outlets grew. 

Further South (about 40 minutes) is Kennbunkport, which offers biking and walking with great views along its rocky shores.  Visitors can admire grand homes of yesteryear, stopping for a meal in those that have been converted to Inns, while also viewing the latest in the highest-end seaside construction.  The town offers upscale boutiques, gift shops and dining.   But Kennebunkport can also be enjoyed on a budget -- it offers what are reputed to be some of the best  fried clams in maine (reports conflict on this controversial issue) at The Clam Shack (on the bridge as you enter town from the South), and at Allison's  Resturant (for those who prefer a table).