A slice of sponge cake and a hearty round of "Happy Birthday" to the Rotherhithe Tunnel! Not the nearby Brunel-designed Thames Tunnel, (the world's first underwater tunnel, lest we forget) but its quieter, lesser-celebrated neighbour that ferries road traffic underneath the Thames from Southwark to Tower Hamlets. It turns 100 years old today.

Opened in 1908 by the future King George V, Rotherhithe was the first road tunnel linking north London with south, and was designed for horse-drawn vehicles, which were in fashion at the time. The shallow gradients at the entranceways are the legacy of such earlier, quadruped visitors. Harking back to an era when Britain was capable of finishing large-scale projects on-time and on budget, the original construction cost £2 million and was polished off 18 months ahead of schedule. Presumably they didn't get Multiplex to do the hard work.

In a century the number of vehicles using the Tunnel has risen from 2,600 a day to more than 34,000. Envisaged initially for use by both road traffic and pedestrians, the noxious fumes from today's horseless carriages deter all but the hardiest of walkers. Step forward Diamond Geezer, who took a stroll through the tunnel earlier this week.

So what kind of party is planned? Well like many a centenarian (not least Buster Martin, legendary Pimlico plumber and marathon runner), the Tunnel's not fussed about reaching such a milestone, and is content to just see out the day doing what it does best: allowing traffic to traverse its 396 meter length.

However, you can celebrate with the Tunnel by visiting its live webcam and seeing what's going down.

Image of the tunnel from Matt Adams' Flickrstream under the Creative Commons Attribution license