The Tubes

From Carpe Chaos

\Many stellar systems are linked together with special devices called "tubehammers." These can be used to travel between star systems much more quickly than one could fly between them directly. Tubehammers push ships in and out of the "tubes," which are a network of 4th-dimensional pathways that can be used as shortcuts to other tubehammers. In order to use the tubehammers, tube-travelers need 4th-dimensional shields around their ships