Some of the most enjoyable things to do while on vacation are free.  Below are some suggestions:

Visit the sand dunes just west of town on US-2. 
Spend an afternoon sunning, swimming, and hiking the winding trails along miles of beautiful sandy beach on the north shore of Lake Michigan.
Location just west of town on US-2.  Over 15 miles of sandy beach.  Your usually able to find a secluded private spot.
 
Free History and Mystery Guided Walking Tours
Every Tuesday, Friday and Saturday evening in July and August at 7:00 pm.
Begins at the Museum of Ojibwa Culture, 500 North State Street
Contact the St. Ignace Visitors Bureau 800-338-6660
Website: http://www.stignace.com 
 
Ride your bike
    * Around Mackinac Island

Mountain bike:
    * On the sand dunes cross country skiing trial.
    * On one of the rail to trails paths. 
    * On one of the snow mobile trails
 
Take a hike
    * St Ignace has a waterfront boardwalk through town.  Historic marker line the walkway.
    * The St Ignace area is surrounded by State and Federal forest land all which are good places for hiking.  So you better take a GPS others like the rail to trails are fairly flat and hard to get lost.
    * The North Country Trail is a National Scenic Trail which when completed will extend across seven states from New York to North Dakota. Today, 1,700 of the 4,000-mile route are completed. Approximately 35 miles of the completed trail lies in the St. Ignace Ranger District of the Hiawatha National Forest.
 
Climb Castle Rock
Castle Rock is rises almost 200' above the surrounding area like an ancient castle of the middle ages. Excellent view of Mackinac Island, Lake Huron and the area.  It is almost free (a small fee per climber). 
http://www.castlerockmi.com.
 
Go See Mackinac Bridge
First visit the bridge during the day time and then come back at night for a even more spectacular view.  The Bridge View Park is located west of the toll plaza. This $1.3 million project includes an observation building, paved access roads, a walking path, picnic areas, trees and landscaped areas containing flowers and shrubs.  After leaving the park take the Boulevard Drive (about five miles) along the lake shore and get even better views of the  bridge.
 
Go Fishing
    * Carp River
    * Castle Rock Ponds (about 5 miles away).  Great for the kids.  The ponds are stocked every June for the Kids fishing derby.
    * St Ignace docks
 
Go on a Picnic 
Below are some of my favorite places for a picnic:
    * The bridge viewing area is a great place.
    * Carp River
    * Sand Dunes
    * Castle Rock Ponds
    * Lake Michigan view area along West US-2
    * St Ignace rest area.  Offers a good view of Chain lake
 
Bayside Live
Every Thursday night starting around the auto show though the end of the summer their is waterfront entertainment.  See the area calendar for details and dates on the various bands, folksingers, storytellers, and comedians that come to town.
 
Watch a Parade
Like most small towns St Ignace puts on a great parade
    * Auto Show Parade
    * 4th of July Parade
    * Truck Show Parade of lights
    * Motorcycle Parade of lights
 
Visit a Lighthouse
See my lighthouse page for a complete list of area lighthouses
 
Watch Fudge being made at one of the local fudge shops
 
Watch Pasties being made at one of the local pasties shops