How to include a file from another folder?

In my current project I have separated my class files and my header files. My project structure currently looks like this:

• Project

• • Source
    • src
      • class1.cpp
      • class2.cpp
    • main.cpp
• • Header
    • include
      • class1.h
      • class2.h

My problem is that I do not know how to include the header files into the class files. Am I unable to link to headers that are not at the same level or in a child folder? Or is there some way to go from the project root and work my way down? For instance:
#include "Project/Headers/include/class1.h" inside the class1.cpp file