Or what appears to be a thin stream of water trickling down the wall…at strategic intervals.
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And then, as the lights in the far distance flicker out, one by one…
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The human cyclopede.
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Point of reference…
https://www.reddit.com/r/askscience/comments/3crbh5/is_pluto_small_enough_that_you_could_obviously/
However, a tunnel is different as you’re not looking at a single vanishing point that’s much harder to see than a large horizon. As you intuit, it would depend more on individual visual acuity, with most unable to see far enough into the tunnel to see anything other than a grey or white light (depending on how bright the tunnel lights are). Not being a biologist, I can’t tell you the theoretical limits of perfect human eyesight in relation to distance.
Edited: My bad, I misunderstood the question.
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Boston’s MBTA Downtown Crossing subway station used to have a pair of wooden escalators which emerged on one side of what was then Filene’s department store where I worked as a box stacker for a season while on a break from college. (edit: a box stacker is someone who literally stacks boxes where boxes need to be stacked within the department store)
In my dreams, when my mind is in need of an escalator, I dream of that place, because the wooden escalators were so rickety and such a surprising one-off that they must’ve left an impression.
That’s a … bike … tunnel? How is that even a thing in this day an age. A true liability and public menace.
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No sorry, I just meant a smooth surface, since I’m sure all the features would make any discernible curvature less discernible. But for some reason the word ‘smooth’ didn’t come to me last night 
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Hey, I think the worse mistake was deleting your answer about standing on a large disc, which was quite interesting and even included a reference to black holes for extra points.
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Great, now you’ve confused Osaka.
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A monstrous gaping crack in the wall should chase away the boredom.
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Like a what now?
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It helps if the tunnel is narrow, since our perception of curvature is partially derived from the asymmetry of the vanishing point. A skinny tunnel has a narrow vanishing point closer to the observer, so you could get away with a lower radius of curvature.
Of course there are patterns that could do a really good job of obscuring the curvature, especially in a tiled tunnel like this one.
Iirc, there are several under the Thames
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what would the diameter of a well-lit circular tunnel like this need to be for its curvature to be imperceptible?
… am I the only one who feels noticeable discomfort when even briefly imagining that?
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The first question that comes to my mind: how was the acoustic?
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Drove through this one a couple of times on a motorbike.
Quite surreal. 3.3 km in a straight line, relatively steep dimly lit with strip lights.
I named two of them upthread. And I can’t recommend the Greenwich tunnel too highly, not because it is by itself such a pleasant experience (after a century it could use a good rehab) but because it is a fantastic way to get to the Greenwich Observatory.
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It’s pretty normal, feels like home.
It needs some decoration. I’m sure the local artists are up to the task.
