180mm Macro is not a bad choice at all. However, for me, personally, I find that a zoom is more useful for landscapes. For that, I'm usually shooting deep DOF, which means I don't need to worry about bokeh or performance at fast apertures, which is what primes are good at. But I do want flexibility in composition -- it's often very hard or impossible to move closer or farther away for telephoto landscape shots - and it might ruin perspective if I did. So I use the 70-200 f/4 L IS. But if you wanted even more flexibility, you might consider the 100-400, which is great for extreme perspective compression. (It can be very hard or impossible to get the DOF deep enough at 400mm, though -- and you want to hide that ugly bokeh.)


But the 180mm may be a better choice for you.