From charlesreid1

Tunnels are a great visual metaphor for thinking about different layers of networking and security.

Partly because software, like geological sediment, has built up over time into different layers, each with its own history, implementation, design, and so on, there are lots of pieces that compose a mental model of networks. Tunnels are a good way to untangle some of those concepts and simplify them for understanding.

First, a Tunnels approach to describing HTTP and HTTPS: HTTP and HTTPS