[thedenimdino]

Another fun fact is that, the doors were built in cooperation between Elves and the Dwarves. Celebrimbor (also the guy who made all the rings except the one) and Narvi.

The friendship between an Eleven and Dwarven kingdom was kinda rare.

And thus, speak friend and enter

[arwineap]

This is going quite deep, is there any chance that Tolkien actually planned for these?

[ReidZB]

Definitely. Enmity between elves and dwarves is a deep theme in Tolkien's world. The Silmarillion presents several in-universe historical events responsible for that enmity. It's also foreshadowed by "God" (Eru) when he grants life to the dwarves.

Friendships between the elves and dwarves are as a result considered very special, which is why Gimli and Legolas's friendship in The Lord of the Rings is such a big deal.