Enzan no Metsuke means that you look at your opponent as if you are looking at distant mountains.
Metsuke is a noun form of "to have your eyes on something" or "the way you see things".
Enzan means "mountains far away from you."
Ok. Basically it means, "look at the whole body of your opponent rather than just looking at, for example, his/her shinai."
So you are paying attention to every sigle movement of your opponent.
You should not look at one part of your opponent or get distracted by his/her shinai movement.
For example, if you are in the city surrounded by tall buildings, you do not see the whole city.
However, if you go up to the top of one of the buildings, you can see the whole city.
When I was in Christchurch in New Zealand, I used to love go up to the hills (Takahe) and look down the whole city of Christchurch.
All the worries I had seemed so small and I felt like I could handle any probelms easily.
You have your opponent right in front of you in kendo. And supposedly in ancient times you and your opponent had a real sword. You need to pay attention to head to toe of your opponet; otherwise, you might be dead.
If you can, try to picutre the background behind the opponent. If you can do that, you can get your opponent at a glance.
If you do, do you just see the car in front of you? Do you ignore traffic light, pedestrian, bicycles and stuff like that?
You try to see the whole view as much as you can, so you are SAFE!
Of course, it is important to see things in details as well, but it is easy to do. Seeing the whole picture is a hard job.
So there is a saying like "looking at your opponent as if you are looking at distant mountains".