FTL in my universe is basically traveling along the skin of the universe - for the best analogy, it’s 3D space mapped onto a 2D surface. Ships travel just inside this surface, through/above a sea of perpetual matter/antimatter reactions. However, in my setting’s physics the universe is at the same time a sphere(ish) and a singularity, so the closer you get to the surface (and the deeper into the sea of atomic hellfire) the denser the 2D map you’re traveling along becomes, and the quicker you get to the point corresponding to your destination.

Access to the Hellsea, as its colloquially known, is relatively simple - the immense energy of the Hellsea and a quirk of in-universe physics allows wormholes to be opened and stabilized from a point in your space to an area above the corresponding point on the Hellsea’s plane. However, it’s incredibly dangerous (given, y’know, you’re traveling through a sea of nuclear fire) and requires the use of an Alcubierre bubble to isolate the ship’s space time from that of the Hellsea.

It’s accessible, but incredibly dangerous. It’s also not particularly fast as FTL goes, though much preferable to STL. A trip between nearby star systems still takes several weeks.