If you want to look behind a sink, into a car engine or somewhere else when you're working on it, a borescope (a lot of people say 'endoscope' but that's a more medical term) is the way to go. I've looked at the best boroscopes, and I can really see the appeal of this one for most DIY enthusiasts.
Simplicity is the key. There is one major caveat to that; Bosch do seem to have quietly updated this to make it more waterproof at some point, and slightly changed by packaging, so do check which version you're getting. If there are two editions of an identically names product at the store you're at, that's why!
