Use plastic poster or pipe roll tube film to create ice pipes for construction. Depending on the length, you could make anything from a fence to a Fortress of Solitude! You can also shape the form into an arc or some such for making a tunnel.

Note: I have previously tried this with long, skinny balloons, but the pressure they generate is a little difficult to deal with. It's hard to transport the full, unfrozen ones without popping them. And trying to fill them in place, outside in the cold, even more so.

Supplies

Pe Tubular Barrel Roll Film Transparent Wrap from AliExpress - about $35

Cold!

(pictured in later steps)

Scissors

Water

Clips or heat sealer

(not pictured)

Plastic tote to protect for pops or spills

Mop or towels for inevitable spills

Step 1: Cut Tube to Desired Length

Cut the tube to the length you want to work with. If you're making a lot of these at one time, I recommend using a large plastic tote and cutting to length so they can fit lying down comfortably inside it. But if you're working outside, the sky's the limit!

Step 2: Clip or Heat-seal One End

Clip one end of the empty tube. If you're using a clip, fold the end over a few times for a better seal. Heat-sealing using a FoodSaver device works even better.

Step 3: Fill With Water

Fill the tube with water (in a safe place to account for spills and whatnot.) It doesn't have to be filled to high pressure like a balloon, just enough for it to pop out the tube into shape. You will need some space at the top anyway to close it.

Step 4: Close Off the Top End With a Clip

You don't want to use a heat-sealer here or the water in the tube might expand and pop it before it's completely frozen. A clip will hold the water in well enough, yet still allow for air to escape. Fold over the top end a few times so it doesn't leak, then clip it.

Step 5: Place in the Cold Area

Assuming you're going to be doing this outside in the winter, it must be below 32 degrees Fahrenheit or 0 Celsius for several hours for the pipe to freeze. Plan on overnight at least. Here is where you make a shape, like an arc. Snow can hold it in place. Just be aware of any kinks in the film as this might provide a weak spot in the finished item.

Step 6: It's Ready!

When the tube is completely frozen, you can now use it for your projects. Use either with the tube intact (you can take the clips off), or take it inside, place it in a bucket or tote, and let its outside surface melt for a few minutes. Then just slip off the plastic film and if you didn't create any holes in the process, you can reuse it!

Step 7: Safety Notes

Of course, there may be safety issues if you make a lot of these and pile or construct them too high. Don't let anyone get inside a structure made with these. Also beware when the weather gets warmer as a piece may collapse. Please be careful!

Nevertheless, whatever you come up with should last for months! (The winter months, anyway!)