Robin Hood’s barn
(n.) an unnecessarily long or circuitous route or means of doing something
We’ve dealt with Robin Hood’s mile before here on HH, but it turns out England’s favourite arrow-firing folk hero crops up in a fair few phrases and expressions in our language alongside that one.
So as well as Robin Hood’s mile (a mile or journey that seems longer than it truly is), he also has a pennyworth (something sold cheaply because it’s questionably made or acquired), a choice (this, or nothing else), and a barn (an unnecessarily long or protracted way of doing something).
(FYI, there’s also a Robin Hood’s wind, but there wasn’t room for that on Twitter. It refers to a biting southeasterly thaw-wind accompanying the end of winter; according to tradition, this was the only wind or weather condition Robin Hood could not stomach.)
But anyway, back to the barn. The reference here is that Robin Hood’s barn—i.e. the land around his territory—was all the open pastureland around Sherwood Forest. To take, or to go by or round Robin Hood’s barn is consequently to take an unnecessarily long and circuitous route. Or, by extension, the phrase refers to a lengthy, time-wasting or unwieldy way of doing something.