Iron Channel

Iron Channel can be considered a true marvel of advanced engineering, created by Mechanics, an ancient and not well known civilization with access to a truly supernatural level of technology and magic. Exact reason for its creation is truly unknown, however it is believed that it was a part of the Mechanic longterm plan of accelerating and helping technomagical progress of Gates of Eternity inhabitants.
To this point an expansive system of channels was created. It connects Native Sea with Red Sea, by extension serving as a connection between Imperium of Karadia and the Eternal Empire in the Far East, together Kasytian Empire, with Yndian states and many spice dealing isles of Lemaria. It is truly massive, with two parallel canals. That can be used to travel in both sides simultaneously. There are also many watergates, operate from the control booths beside it.
It is practically vital to continuous existence of modern economy, with taxes on goods transported through this place being a substantial part of the budget of Imperium of Karadia, despite not being that high (and in fact rather modest). The sheer ammount of money that can be gained from control over it being a cause for multiple wars during the history.

Alterations

The biggest problem with Iron Channel is that it cannot be in any way altered. It was built to serve certain purpose and the alterations to it were never a part of Mechanics plan. It is made from a dark material that cannot be even scratched by overwhelming majority of materials known to civilizations of today.
Few toughest actually can do this, but... the material is made to return to its original form. Noone knows how it works, but it is hard to add anything when all nails and things like that that are used on it soon disintegrate.
On the other hand it also means that all damages that happen to it are soon automatically repaired. Which means that blocking passage through the Iron Channel for long is impossible.

Type

Canal