Edit: edits inspired by @TzeraFNX's suggestion
Suppose we have a pocket dimension or alternate dimension that's accessed a bit like Narnia, by having very subtle portals in various secluded places (remote rural forest roads, the inside of a large coat closet, etc) that are passed through when moving in a specific direction, in a specific context, etc, while in other cases, one passes by the portal without noticing anything unusual.
In particular, observers who aren't entering the portal should not be able to see any objects entering the portal (rather, they enter a secluded space and mysteriously disappear when nobody is watching them) and nobody should ever see a clear portal boundary or surface (the exact opposite of, say, a stargate ring or the blue and orange boundaries in Valve's Portal and Portal 2), or see the enchanted world from a standpoint that's completely in the normal world.
By this method it's possible to allow personnel and vehicle access to our enchanted land without people noticing what's up. But aircraft access is a bit harder, unless you resort to landing them and then taxiing or towing them along the aforementioned secluded forest road, which I don't (and which tends to subject itself to nosy people looking at aerial photographs).
Does anybody have a clear idea of what we want to do here?