This arch is between a path and the railway line; for context, see
NS3879 : Old gate and archway and
NS3879 : Path to Burnbrae.
It is probably a remnant of one of the buildings associated with the old Millburn Pyroligneous Works (whose former site is now occupied by a depot:
NS3879 : Millburn Roads Depot). The Vale of Leven website has a page –
Link – with old pictures of the works. Photo 11 on that page shows some arches in the background, similar to the one in my picture. However, the one in my photo is on the other side of the railway line, and not below it; it is most probably not far from the arch that is on the right in the old photograph.
The other two arches in the old photo, the pair on the left, are still present, and can be seen in
NS3879 : Railway underpass; the path now leads through the one on the left, and the burn flows through the one on the right (that arch is harder to see because it is obscured by the modern fence).