Single page on a different wp theme

Hello,
I have a wordpress website hosted on a personal domain, the entire website uses a template with its custom header, top menu, sidebar, etc. and I want to create a single page without this template and all of its elements.
This page has been thought as a portfolio created with Visual Composer elements and it has to be accessible from the menù of the main wp website, described just above.
What is the best way to achieve this?
I thought about installing a second wp installation and creating a page without a template linked to it.