The World is our own with some modifications, which are basically the modifications that are also used in the Marvel Universe. All demigods and mythic gods really exist, except the creator of the universe. All these gods are are connected to earht via a Cosmic Axis. There are also a lot of alien races who monitor Earth, because of the supernatural beeings, the Cosmic Axis and a warp nexus in our solar-system.
Due to experiments of an alien race called the Celestials in the early days of human-history until today , many people are able to withstand deadly poisons, stress or radiation and build up supernatural powers as a consequence.
The technology is more advanced than it is in our own reality, but most of the advances are done in secret. Some people are also doing Magic, or are affected by mystic beeings. It is also possible for normal people to build up in combat or other fields of activity, like Captain America.
There exists also an infinite number of dimensions beside our own. These contain other timelines, alien places...Some heroes are able to travel to other dimensions. The dimension Crossroads links all the other dimensions together. Crossroads can be visited, too. This place is a infinite combinations of path, each of them ends in a dimension.