The old railway bridge and viaduct cross the Namoi River near the showground, a remnant of the Barraba Branch railway line. It is not a grand monument, but it gives Manilla's transport history a visible edge and makes a useful short walk from the town centre.
The bridge is best paired with the river rather than visited as a standalone sight. Walk down in daylight, look back toward town, and you get a quick sense of why Manilla sits where it does: roads, rails, and rivers all meeting in one small inland place.