Underground routes can be referred to by a variety of different terms. Some of the most common synonyms include subterranean passages, subways, tunnels, catacombs, and secret tunnels. These different terms can be used to describe different types of underground routes. For example, subways generally refer to transportation systems that run underneath city streets, while catacombs typically refer to ancient burial sites that were built underground. Similarly, secret tunnels might be used to refer to hidden tunnels that were used for military purposes or to smuggle goods. Whatever the type of underground route, there are many different ways to refer to it, depending on the context and intended meaning.