Armory3d is a completely open source game engine that is fully integrated into Blender. Below is my first attempt at stitching a terrain mesh, layered with satellite/flown imagery, making use of the excellent BlenderGIS plugin. You can then simply export the project to an HTML5 application which can run on any browser.
See below a second attempt with some slightly higher resolution sat data, with some improvements to control methods (detailed below). Use WASD keys & left mouse button for controlling camera, sun direction and shadows can also be adjusted with keys – T,Y,G,H,B,N:
Another example including some building OSM data overlayed across the terrain:
I’m still working on perfecting the movement controls within these terrains, but using elements from the handy Logic packs created by the community, I was able to form the following controller setup within Blender:
This allows for smooth follow WASD keyboard movement, combined with mouse middle button/left click for free look & rotation.