Q:

Is it "en route to" or just "en route"?

I have often come across various posts that people make on any social media platform as, for example:

En route to the Taj Mahal.

or

En route Paris.

Although what I have been taught that it always has been only 'en route', without 'to'. What I feel is that it's a mass-mistake committed by so many people, that they have started to believe in the fact that it's also true (i.e., 'en route to').
Hence, I would like to have an even more expert view on this.
Although, I myself have done a bit of my own research:
-Historical comparison of en route to vs en route

So my inference has been that:

As the meaning 'en route' itself means while travelling from/to a place, hence, it's useless to add to in any sentence.
If one would look into the historical data, especially of British English, provided by Google, then both the words have been in existence but the mostly the old school writers prefer to use only en route instead of en route to. This can be easily distinguished by the usage of both of these choices.

Thereafter, I would like to finally know that if my research and inferences are correct.

A:

It depends. If you are "en route to the party," then you use "en route to." If you are "stopping for lunch en route," then you use "en route." 
Dictionary.com shows the "en route from" sentence structure and the "en route" sentence structure: "The plane crashed en route from Cairo to Athens," and "He reads en route."
Merriam-Webster shows the "en route to" sentence structure: "I finished my homework en route to school."

