Journeying is a central part of my novel. However, it gets really boring really quickly to describe them walking through the same landscape for a few weeks. I want to skip to the parts that are interesting to keep readers engaged, but I am afraid this will limit the sense of scale of that journey. It's difficult to find a middle ground between portraying days of journeying in the cold harsh weather and then their relief when they reach a village. How do I manage to skip over most of the journeying while still impressing the general feeling of that journey?
Just say that they walked for two weeks, but throw in a few interesting tidbits about the journey. The longer the journey, the more details you add. Don't just write;
"Alright, to mount death we go!" I said. We walked for two weeks, arriving breathless from the travel, blahblahblah...
Write something along the lines of;
"Alright, to mount death we go!" I said. We walked a long time, Passing the occasional farm house and small town. Gerald kept falling into the odd potholes, and his shoes were constantly squeaking from the water in them. Paula and Henry were definitely getting closer, I could tell that much just from their general behavior. I noticed Steve was staying quiet, having not said much ever since he had been mind controlled and nearly killed us. It felt like we had barely walked at all, but when I looked up one afternoon two weeks later and there was it was, the gate to mount death.
This way it takes a bit longer to read and the reader can translate that a lot easier to the two weeks travel to mount death. Once your characters arrive at mount death, you can go right back to the interesting stuff and shooting everyone.
As an added bonus, you can also drop subtle hints about any characters that might be a spy/bad guy/clone/something like that without outright saying it.
In addition to summarising the entire journey (examples provided in @Ceramicmrno0b's answer), you could also include several smaller time skips connected by significant events described in more detail. You'd summarise the first leg of the journey, then, for example, describe the scene of how they almost got spotted by scouts and little Timmy, previously seen as a hindrance, saves the day. (That kind of character development should not be hidden in a summary.) Once that scene is resolved, you can summarise the next leg of the journey, followed by another significant event, and so on.
And the summary doesn't have to be bland, either. Ideally, the summary would lead over to the event you're going to describe in more detail.
Two weeks after we left Fort Hometown, we started to notice a suspicious lack of animals. It became harder and harder to catch any wild rabbits or birds, until at last we were forced to dig into our rations to supplement a diet of grass and moldy-tasting roots. So when, after a few days of absolute silence, I heard the distinct chirping of songbirds in a clearing ahead, I first thought my ears were deceiving me. But my companions' faces betrayed the same sense of wonderment and relief I was feeling. Simon rushed on ahead, but Jane held him back with a warning finger to her lips. [leading into the actual scene]
Of course, if the journey is uneventful, skipping it entirely is also an option. This holds especially true if the narrator has done the same trip before.
Once again, we set out for Shangri-La. But this time, we were not only armed with foreknowledge and a map, but the snow had melted and the roads would be clear. And as the saying goes, "Once you've found the way to Shangri-La, you'll never lose your way again." [new chapter] The evening sun glinted off the roofs of the ancient city when we finally arrived, exhausted but glad to be back.
Journeying is a central part of my novel.
A good, traditional theme from the Odyssey to Tolkein.
However, it gets really boring really quickly to describe them walking through the same landscape for a few weeks.
Well, then your job is to make it interesting. There's an entire genre devoted to making travel interesting: nonfiction travel writing.
Travel is a great opportunity to see various sides of your characters. How do they deal with adversity and being stuck with each other? Adversity doesn't have to be big, but it can trigger character faultlines. Who has to do the cooking, washing up, horse maintenance, railway scheduling, or whatever minor domestic details get in their way? Do they meet anyone along the road?
What happens if the characters get bored? What do they talk to each other about? Do they miss their homelands? Do they anticipate or fear the destination? Do their buried worries surface? Do they fall in love or grow to hate each other?
Do they tell stories to one another? (Canterbury Tales). Do they sit around the fire and sing songs to one another? What about? (Don't put the actual songs in unless you're Tolkein)
Remember that one of the great plays could be accurately summarized as "two old men sit on a bench and wait for someone, who does not arrive". External action is not required to make something interesting.