When walking I find it helps if you keep your eyes moving, mindfully noticing your surroundings and the horizons in front of you. It's very easy to get focused on the specific spot on the horizon you're walking toward or, worse yet, to start looking down at the pavement right in front of you without ever looking up. That's when boredom really sets in. As long as you're looking around and noticing things and wondering about them or making up stories about them, it pretty much keeps boredom away. But if you walk the same route in the same direction all the time, that gets boring really fast even if you're being mindful.