By the end of July my husband and I, like most Minnesotans, were starting to tire of the heat and humidity. A trip to the rocky cliffs and crashing waves of Lake Superior's North Shore was calling and, even though we had not made reservations for a campsite on a busy summer weekend, we headed north with our camping gear in tow to see what we could find.

Minnesota's scenic North Shore is a siren song to harried urbanites all year round but particularly in late summer when the cool breezes off the great lake mix with balsam, pine and campfire smoke and the warm sun helps you forget how cold that lake really is. The hot ticket item is a tent campsite right along the lakeshore. None are more in demand than the 20 cart-in sites at Split Rock Lighthouse State Park, where each secluded site has its own share of Lake Superior.

We set our sights on Split Rock on a Sunday morning. Why not go for the most popular tent campground in the state during the high summer season without having made a reservation? In for a penny, in for a pound; shoot the moon; bet the farm ... what did we have to lose? We were prepared for, and open to anything.

"You are in luck," assistant park manager Lisa Angelos told us at the park office. "Hard to believe, but two sites opened up this morning."

Split Rock's cart-in campground is a hybrid of car camping and backpacking. You roll your gear to an assigned site using a cart provided for that site. The sites are spaced farther apart than at other campgrounds, giving them more of a backcountry feeling without having to sacrifice access to your car or amenities such as hot showers and flush toilets. The restrooms and showers are located at the parking area and cart corral and are within one to four city blocks of the campsites.

Each campsite is equipped with a leveled tent pad, a picnic table, a fire ring with a grill and a bear box for storing provisions. Water is available at the parking area, and firewood and ice can be purchased at the office.

We set up camp at our site above the lake with a view of the historic lighthouse through the birch trees and spent two glorious days exploring the park and the lighthouse. We hiked the park's 14.5 miles of trails along the lakeshore and inland along the Split Rock River, stopping to cool off in its many waterfalls. That first evening we enjoyed a beautiful full orange moon over the glassy lake at our campfire.

The next day we toured the lighthouse and visitor center (1-218-226-6372; $8 adults, $5 ages 6-17; free for ages 5 and under and Minnesota Historical Society Members). We biked along the Gitchi-Gami State Trail, a hilly and strenuous but paved segment that runs the length of the park along Hwy. 61.

Here are some tips for a spontaneous North Shore camping getaway:

Think outside the box

A long weekend doesn't have to start on Friday. While reservations are a must at the most popular state park campgrounds, sites do open up, and you can call ahead to the park office to find out about any cancellations that day and reserve by phone. By starting early Sunday we could take advantage of openings that occur more often on that day; we avoided heavy traffic and we still had two full days to enjoy the park.

Be willing to hike

Come prepared for any outcome. We had brought our backpacks and were prepared to hike into a site if that was all that was available. There are four backpack sites at Split Rock and several walk-in and backpacking sites at state parks farther up the shore, as well as at state and national forest campgrounds inland. If you can't get a shoreline site at the last minute, you can find a secluded site not far from the big lake at any time if you're willing to work for it.

Let your fingers do the checking

Check online early and often. Even if you are doing a spontaneous getaway you should check availability online before you leave so you know what your odds are of finding a spot at a specific campground. The national forest campgrounds also take reservations online and the most popular sites are reserved early for weekends. In the age of mobile technology, you can check your iPhone on the road to see what's open...hmm... maybe there should be an app for that?

Be ready with backup

Have a Plan B if there is no room on the shore. Know where the best backwoods sites are on the North Shore. An excellent resource is "Camping the North Shore" by Andrew Slade, which has many good tips on finding secluded and scenic campsites all along Hwy. 61. You might want to make a reservation at a hotel that you can cancel just in case you can't find anything and you don't end up in your car late at night.

Laura Merriam is a freelance writer based in St. Paul.