A Webway Gate, as its name suggests, is an opening of the vast Webway network. Also called the Nexus of Webway Gates or the Webway Nexus, Webway Nexuses are also found scattered on worlds throughout the Galaxy, allowing the Eldar to travel to many planets. They are constructed primarily out of Wraithbone and can vary in size, from small individual gates to ones big enough to fit a Battleship.
Among the greatest of these belongs to Alurmen, whose Nexus was unmatched by the other Craftworlds. Through its Nexus, the inhabitants of Alurmen could send explorers and traders with an ease that was second only to the Old Ones. Its Nexus of Webway Gates allowed it to be connected to other Craftworlds, Exodite colonies, Maiden Worlds, and other ancient Eldar sites making it Craftworld Alurmen's greatest strength as well as treasure.
Around four thousand years ago, during the Age of Apostasy, Ahriman learned of the Nexus and intended to use it to travel to the fabled Black Library of Chaos. Learning of this future, the Farseers of Alurmen decided to hide their Craftworld in order to protect the Webway Nexus as they knew they could not fight the Sorceror. In desperation, they severed ties with the other Eldar and sent Alurmen into the Cerberus Shroud where they activated an ancient C'tan devices designed to suppress the power of the Warp thus hiding them from Ahriman's mystical sight but at the cost of being damned by the rest of their race for using Yngir technology. Why they decided using a fucking C'tan of all things, we have no idea.
Their efforts saw them and a Chaos fleet being entrapped within a Warp barrier around the Shroud Nebula thus preventing anyone from gaining access to the Webway Nexus.
Has the Aeldari keyword and gives a couple of unique stratagems, so it's already more synergistic than many of the other building options. It has a special rule that gives it the equivalent of Infiltrate and units aren't embarked within it but instead may teleport from any Webway Gate.
This is generally more of a liability than a benefit, as it can result in being locked out altogether and prevents you from firing out of it. Units also disembark one at a time, which can give you a larger "transport capacity" than other buildings, but it is less helpful for deploying characters. The gate has an invulnerable save, but has fewer wounds and toughness than buildings of a comparable nature. Best used in multiples (even having six wouldn't be completely crazy in larger games) as it lets you strike from many potential places and helps prevent getting locked out if they're destroyed.