In Serious Engine, physics is demand based. Also, gravities of different directions are supported, and objects can be oriented differently. They don't always have to be standing up. If you stand on a rocking boat, your view rocks too, if you are catapulted, you can fly with the head first, etc. Serious Engine has ray-casting functions callable from entity AI with several customizable precision parameters.
Rays can be infinitely thin or of custom thickness.
Serious Engine has specific support for several key-features that enable creation of large worlds. That includes multitexturing, autoanimations, specially optimized physics, heavy use of LOD techniques etc. Serious Sam game actually does include levels that cover 100 square miles area. In the game, you don't actually walk around all that area. You just sail in a ship along, and all the rest is scenery.