In order to classify something as a spectacle, one must know exactly what a spectacle is. By definition, a spectacle is "a visually striking performance or display" with the Latin roots meaning "to look" and "public show." This is precisely the category that Bath and Stonehenge fall under; two very different places, but each a spectacle in its own regard.
Upon arriving in Bath, it becomes quite clear (depending on the weather) just how much the city alone is a spectacle; small, filled with centuries of history, one hundred miles outside of London with the tranquility to prove it. Right outside of the Roman Baths, there was a woman singing the most beautiful sounding Opera music that seemed to suit the city so nicely, as if that kind of music should be playing on a track every day, if only for ambiance.
The Roman Baths alone were a spectacle, and are the reason behind the city's name. Built around 60-70 AD with several developments in years following, many of the original baths and architecture still remain (of course with some redevelopment along the way, as preserving such an elaborate place is no easy feat). The most intriguing and visually stimulating of the Baths (up for debate) is the Great Bath, which at one point in time had a roof over it. What is particularly fascinating to learn is that Bath houses, such as this one, were a place of communal activity, not merely a private hygienic obligation as it is today. Bath houses were a source for social gathering and relaxation, and still are in many places, such as the bath houses in Turkey, a custom that dates back several centuries. The Great Bath is quite a spectacle, although the green water isn't too inviting for a swim. The roof that once covered this bath would have protected it from things such as rain, sun exposure, and other natural elements.
What is so rewarding about seeing a spectacle (besides, of course, seeing the spectacle) is being a spectator. A spectator is someone who views or watches, and hopefully what they are watching is something spectacular. Without the spectacle, there is no spectator, but without a spectator there will still be a spectacle. Stonehenge will still be fascinating regardless if there are people to watch it. We cannot be spectators without having something to watch. It's almost like the "if a tree falls in a forest" question. Of course it will still make a sound even if no one hears it fall, and Stonehenge will still be a spectacle even with no one to see it.