(Building on a bit of discussion from here: Are the "wood between worlds" and Aslan's Country related in some way? )
In the Chronicles of Narnia, it is well established that Aslan's Country (meaning heaven) is located across the sea from Narnia proper. However, in The Voyage of the Dawn Treader Aslan tells Lucy that there is a different way of getting to his country from our own world:
... I will not tell you how long or short the way will be; only that it lies across a river. But do not fear that, for I am the great Bridge Builder.
Since I was a child, I have wondered what the heck he was talking about. There is no association that I know of between our world's version of Aslan (i.e. Jesus) and river crossings or bridge-building. (If the way had been via a ladder, it would have been an obvious reference to Genesis 28.) Yet I cannot imagine that Lewis was not alluding to some specific theological concept when he wrote this. So what was the theological reference he intended here?