The Newhaven universe is an alternate reality. It is more-or-less Lovecraftian and loosely based somewhere from the 1920s to the early 50s, the culture being a mix of both the US and the UK. However, other pantheons and monsters are well represented.
The port of Newhaven is based on a simplified version of a map of Arkham. In 28mm, Arkham itself would have been a bit much. It is on the Miskatonic River and includes one campus of the Misakatonic University. It is not certain whether it is the same Miskatonic described by Lovecraft, probably not. There are many different universes in many different dimensions. Some of these different universes, etc, are actively studied – both officially and unofficially – by the university. This can have consequences.
Newhaven – as well as many other places on this Earth – has a slight problem. Some of those different universes/dimensions are very close and they sometimes ‘leak’ through. Not all the monsters come from other dimensions though. The Newhaven universe is large and the laws of physics there allow creatures to reach Earth from places like the Crab Nebula or Orion via wormholes. Some don’t need wormholes – they fly here all by themselves.
There are military differences between our universe and the Newhaven one. The authorities are well aware of the status of their planet, especially in relation to the undersea denizens. Like Innsmouth, a few years previously certain reefs of the coast were depth charged by the navy. Since then, a new class of small coastal warships has been produced to protect the coast. These are the Arkham class, and exist in 3 (for now) versions: gunboat, torpedo boat and anti-‘submarine’ boat. At least one gunboat and one anti-submarine boat are usually based in Newhaven itself. However, the government is probably not aware of the degree to which the undersea world has infiltrated the land, especially in relation to various religious organisations that worship or ally themselves to the undersea peoples.
Some of the other dimensions closest to Newhaven are almost supernatural in our terms. By supernatural, they and their occupants seem attracted to religious sites such as churchyards. These churchyards may be the site of interdimensional breakthroughs or even provide a permanent home for… creatures. Such creatures dislike being disturbed, which can be awkward, especially if a graveyard is deserted then later, perhaps, built on.
Other creatures will have their own limitations. Some may find the energies given off by religious sites and objects to be painful or even fatal. For these, religious artefacts can be used as weapons. Some sites and objects can draw on arcane energies to ‘create’ creatures. Thus a creepy wood may create hostile treemen, a graveyard create ghosts, lamias, etc.