I know that you can't just let a husky run free, so how do you satisfy their need to run/explore?
Luckily we have a really big backyard and Blaise loves to run around it with the kids.
We took a walk the other day and went onto a little wooded path and Blaise wanted to just take off so badly! I was trying to think and wondered if people sometimes just get a really long line and let them go as far as it will let them. But then I thought it could really get tangled in trees and things.
Any suggestions?

We let our 5month off all the time, usually at an enclosed park only. I always take a pouch with treats in and let her know I've got them so she will come back to us when called. This however is at your own peril as sometimes she will decide that a dog on the other side of the park is more fun or she just gets into this stubborn "I'm going to explore over here now" and not come or be interested in food even when I get close enough to show her it. I've also tried long 15meter leads and do find they are a bit of a nightmare to manage when you have trees or other dog leads in the way.

Boy, oh boy! My Mini-Schnauzer is perfect off leash. However, with all the training, sit, stay, heel, come... The first time I let Zhukov, our Husky, off leash, he was GONE! BANG! Took off running like there was no tomorrow.... Never again.

He will come and sit right next to me in the yard, but I will never trust him again out in the big wide world.

Mine run like mad around our yard that's around an acre in size. I also bike mine. If over a year old biking is a good option to really get those legs stretched.

Blaise, I had one girl who I let run because she was excellent about coming back - even when it took her several minutes to make the trip - until one day she didn't. Huskies are bred to run and given the chance, they will run! To put it simply, anytime you willingly let your dog off lead you're potentially taking your pleasure and the pups life at risk. I've lost one and won't lose another.

They can get plenty of exploring done at the end of a leash. And letting dogs poke around a bit during walks is good mental stimulation.
As for running, find an activity you can do with them that lets them really stretch their running muscles. Jogging, biking, skiing, etc.

Finding large fenced in areas like dog parks could give them some room to be free. You could try working with an ecollar. But you really need to do a lot of training to make that work, and even then, for a husky I would make sure the area where you are letting them off leash is free of distractions (other dogs, people, small animals).

Like others have said though. Huskies are innate wanderers that don't always take well to listening. Any time you let one of leash, you are running the risk of never seeing them again.

There is also invisible fence...when out and about, I use a variety of leash lengths. For trails, woods, I use a 12 ft leash that I made. Ami is good at not letting obstructions get between he and I. On country roads with little traffic I use a 30' long line.

How old is your Siberian? If he/she is 18mo+ perhaps you can look into bikejoring. I know my dogs love it after a nice 6 mile run in the mountain bike trails. Of course weather has to be cool enough too.

I had one husky that I could walk off leash, he was special though, incredibly loyal and preferred to be by my side instead of with the other dogs. But that is rare. What I did with another one of my huskies is tied her up to my yard dog, he kept her home, but I would still be outside with them to keep an eye on them because if a cat or rabbit came bounding around, they were both after it. Otherwise, like Amy said, just different lengths of leashes. My dogs figured out how to untangle themselves when they got stuck. The more often you do it, your dog will know what will get them stuck and what won't.