When the forecast calls for snow, children rarely greet the news with anything other than exhilaration. A good snowfall doesn’t just mean that school might be canceled for the day. It also brings a chance to go sledding, build snowmen, and enjoy the activities you can only do for one season of the year.

Snow forts have long been a productive way to make use of a blizzard’s bounty. These icy structures can be used as defensive parapets in snowball wars, or they can simply be places to get out of the wind when playing outside. You might limit them to a wall or two, or you might create a larger fort with multiple rooms.

Make a plan. Before you start building a snow fort, sketch out the shape of the fort as well as any features you’d like to add. If you want to try sculpting snow to incorporate interesting designs and shapes into the structure, draw these out as well so you have a template to work from.

There’s plenty of room for creativity in building a snow fort. The Kemi SnowCastle, an annual attraction in Finland, is large enough to include a hotel, restaurant, and chapel, all made of snow and ice. The Kidtopia Snow Fort at Keystone Resort in Keystone, Colorado, claims title to the largest dedicated snow fort in the world; the enormous structure includes slides, tunnels, towers, and other features meant to encourage fun.

Build in optimal conditions. Constructing your snow fort when the temperature is consistently low will help it last longer. Construction on the Kemi SnowCastle begins when the temperature falls to at least -7 degrees Celsius (19.4 degrees Fahrenheit). Wear appropriate winter clothing such as gloves, a hat, and a warm coat while building, and take periodic breaks to warm up.

Choose a level surface to build the fort. This will make it easier to build the walls and help keep them stable.

Outline the area you’d like the fort to cover. Sticks work well for this purpose, or you can simply trace lines in the snow. You should also be careful about where you locate the fort.

“Think about building it in an area where when the sun breaks, it won’t melt your fort,” says Russell Carlton, spokesperson for Keystone Resort. “Think of those spots in your yard that always tend to be in the shade.”

Materials matter. The best type of snow for fort building is slightly wet and well-packed, allowing it to remain more cohesive. It should be free of air pockets, ice chunks, or debris such as sticks or rocks.

One way to build a snow fort’s walls is to excavate the interior area and pack snow around the perimeter. Keep building up the base so that the upper part of the wall will be well-supported. Another option is to roll large snowballs up to the fort’s perimeter and add on to them.

Build it to last. If you want a particularly large fort, you might even bring in heavy machinery. Carlton says the Keystone Resort snow fort this year is 100 feet long, 60 feet wide, and 15 feet tall; snowcats are used to pile up the snow, while people use tools to further shape and sculpt the fort.

You can give your fort more of an interesting look by stacking up bricks of snow. Rectangular containers are ideal for this purpose, including plastic storage boxes and coolers. You can also use other containers, such as sand castle forms, to create different shapes.

Simply pack the snow into this form and then carefully work it out of the container in the preferred location. If the snow is powdery and dry, you can collect some in the container and mix in some water so it will pack better.

For the next level in the wall, put down more snow bricks on top of the ones you have already laid. The bricks should alternate, giving them the appearance of a brick wall, in order to improve the wall’s strength. You can stabilize the walls by packing snow into the gaps from the interior, leaving the brickwork appearance on the exterior.

Once the fort is constructed, add water to the walls. This will quickly freeze in cold temperatures, further strengthening the fort. Water should be added from the bottom up to keep the walls from getting top-heavy and collapsing.

Accessorize! Water dyed with food coloring can be sprayed on the fort to give it a more vibrant look. You can also use LED lights, which will illuminate the fort without putting off too much heat.

Other materials can be incorporated into the fort to make it more interesting or shorten construction time. Old windows can be used in the walls, or snow can be piled around the sides of a pop-up tent to give the fort a roof.

If you just want a defensive bulwark for snowball fights, you can stop after building a wall or two. For larger forts, you can let your imagination run wild with turrets, snow benches, and other features.

Make sure the forts aren’t located too far apart if you are planning to lob snowballs between them. Alternatively, you could leave more space between forts to use them for a wintry game of Capture the Flag.

Be safe and sound. Simple forts are generally safe, but more complex ones can be dangerous if you aren’t careful. Roofs and tunnels made of snow can collapse and trap you inside. You should also build the fort a safe distance from the street or driveway, since a snowplow operator might clear the area without realizing that people are playing in the snow.

In the Kemi SnowCastle, no support structures are used. However, large molds are used to shape the snow, and they are not removed until the snow has hardened. Walls are 1.5 meters thick, and the SnowCastle is further stabilized through the use of snow arches.

An easy way to build a more substantial fort without compromising its safety is to pack snow around a more solid form. Wooden pallets can be a useful building material for this purpose. You can arrange them into rooms, cover them with tarps or plastic sheeting, and cover them with snow until your fort is complete.

This type of construction is used to build a large snow castle at the SnowKing Winter Festival in Yellowknife in the Northwest Territories of Canada. Stephan Folkers, who works on the festival, says plywood forms are used for the walls and other structural elements. Powdery snow is then blown and compacted on these surfaces.

Snow blocks made from large square forms are also used in the castle, along with blocks of lake ice used for windows, countertops, and other features. The frigid temperatures in Yellowknife freeze the fort into a solid “snowcrete.” The castle opens in March and closes a month later when the snow starts to melt.

“If your winter is cold enough, you can build a safe snow structure,” says Folkers.