Any acoustic space in your own recording studio
It's amazing how different rooms and spaces have their own particular 'sound', and how the ear immediately recognizes and appreciates this. Music has always developed in correspondence with the acoustic spaces available and in common use. Organ music, for example, generally has slowly changing harmonies that suit the long reverberations times of churches and other large buildings in which organs are generally found.
Since the early days of modern popular music recording, engineers have sought to provide reverberation on their recordings equal in quality to the best acoustic spaces. But unless you actually take your equipment to such a space, then the best you can hope for is a pale imitation.
Even the best digital reverberation processors struggle to imitate real acoustics, particular small rooms and spaces, which are the most difficult.
But now there is a better way - the 'convolution reverb'. I don't know why they called it that - it should have been called the 'sampling reverb', which is what it is.
So imagine that you discover by chance a remarkable acoustic space (I once visited a disused brick kiln that sounded like nothing I have experienced before or since). With a sampling reverb processor, you can capture the acoustics of that space for later reuse in your own studio.
To capture an acoustic, you need an 'impulse response'. This can be recorded in two ways - one is to fire off a short, sharp impulse into the environment and analyze the resulting reflections. The other is to use a gliding tone and a tracking filter to analyze how each frequency interacts with the space.
Either way, these impulse responses can be stored and shared. There are already libraries of responses that can be used in sampling reverb (sorry, must remember to say 'convolution reverb') plug-ins, from the insides of vans to concert halls to places where you would only get the chance to visit very rarely.
It's a great idea and fun to use - with some systems you can even sample your own acoustic spaces. I would class it as one of the true breakthroughs in recording technology, as great a breakthrough as sampling itself.