Two Themes In WordPress?

Hello,

I have a pretty basic blog site set up WordPress 4.0.1 running Twenty Twelve Child theme, it’s basically a few pages and the rest are all posts.

I want to create a new page but that looks totally different to the rest of the site (almost as if it was a different website). I would probably use Twenty Twelve or similar for this and create a new child theme to tailor it to how I’d like it to look.

What is the best way of going about this?

Thanks,
Alex