I’ve posted earlier about synesthesia, which is a mixing of senses that some (surprisingly many) people have. Of one of the trailers in the post, you can see now the full version – it looks fantastic.
Took them a looong time to make the 10 minute movie, since synesthetes have very specific sensations. They are very individual, but there are also tendencies – for example that high sounds have bright colors.
You may be even able to learn some synesthetic abilities. There is some interesting ongoing research about learning to see colored letters.
The color blind Neil Harbisson took the idea of intentionally mixing senses even further. On his TED talk you can see how a device he’s wearing constantly converts sounds to color – and he also uses it to make art.
By the way: if you know children that (perhaps) have synesthesia, you can help the research on this topic. Maybe it helps the child too.