A helter skelter1 is a type of amusement park ride that was popular in Britain from around 1906 through the 1960s. It consists of a long slide spiraling down around the outside of a tower, which one would ride down on a burlap sack or a mat. The name of the ride comes from the much older phrase helter-skelter, meaning to do something in a haphazard manner or in a confused rush.
While the first recorded use of the term to refer to this type of ride was at the 1905 Hull Fair (photo), rides of this general sort had certainly existed before this (historical records of fun slides are surprisingly lacking). In 1906 a number of other slides appeared in the UK under the name helter skelter, and it is not entirely clear if these are new constructions or simply rides that have been opportunistically renamed.
It is worth noting that the first ride of this name was not a spiraling slide at all, but appears to have been the serpentine Helter-Skelter slide at Coney Island's Luna Park, which opened in 1903.2 Like the later British helter skelters, you grabbed a coconut mat and slid down a slide, but this slide was a fairly tame trough that cannot honestly be described as 's' shaped, unless one is refering to a long S. The term atrophied in America and become increasingly popular in the UK, and now it refers exclusively to spiraling slides.
The traditional helter skelter is a squat, brightly colored tower looking something like a stumpy lighthouse.3 They are usually painted in a style best described as 'carnival', with blinding stripes, although anything eye-catching will do. They are usually wood or aluminum, and the slide is traditionally laminated wood, although as you might imagine this is less common in modern helter skelters. The slide traditionally makes only two full circuits of the tower, and is slightly less steep than the average playground slide;4 not to worry, you have mats that let you go faster, and plenty of time to pick up speed. For safety reasons, the slides have high sides, and modern ones may be fully enclosed.5
While I have found complaints online that helter skelters are vanishing, the truth may be that it is only the lighthouse-shaped towers that are disappearing. Modern slides built around a fairly utilitarian (but brightly colored!) scaffolding provide a more mobile structure for the modern traveling fair. Festivals with a bigger budget can (and do!) rent an old-style tower adorned with thousands of lights. And you can still find the traditional version at many permanent amusement parks, particularly those aiming for a retro vibe. And yes, Dreamland Margate still has one.
1. AKA a toboggan slip, lighthouse slide, and lighthouse slip, among various other names.
2. Nicknamed the 'Electric Eden', Luna Park was quite modern, with tons of lights! It is quite possible that much of the attraction of their Helter-Skelter was in the fact that you rode to the top in an escalator, the first escalator open to the public having only been installed a few years earlier in 1896 (also, as it happens, on Coney Island). The first one using proper stairs, rather than a simple incline, appeared in 1899, and was a big hit at the 1900 Paris Exposition Universelle.
3. As best as I can find, the 'traditional' helter skelter is the 1920 tower from Dreamland Margate, which has been a template for many modern rides seeking to evoke nostalgia. It was white with undulating orange vertical stripes punctuated with yellow diamonds, with a red slide and a red and white striped cap for a roof. The windows at the top are modeled on middle eastern arches, although the entrance at the bottom of the tower is pure carnival attraction. It has an enclosed walkway extending halfway around the top of the tower.
Postcards showing helter skelters from 1906 suggest that the towers may have been constructed from brick, and they were not brightly painted; in the public's mind, traditional does not mean in the style of the originals.
4. I estimate the average slide to be at about a 15 degree slope.
5. If you would like to see a good assortment of helter skelters, this is a good site. The first picture, and then the fourth picture on the second page, are perhaps the best examples of the Dreamland Margate clones.