BlueMap is a tool that generates 3d-maps of your Minecraft worlds and displays them in your browser. Take a look at this demo. It is really easy to set up - almost plug-and-play - if you use the integrated web-server (optional).
The Sponge/Spigot-Plugin automatically updates your map as soon as something changes in your world, as well as rendering newly generated terrain and managing the render-tasks.
Some features and some blocks are still missing. Especially some tile-entities will not render correctly/at all. Here is a list of what is planned for future releases.
You can download BlueMap from here!
BlueMap can be used on the command-line, or as a plugin/mod for your Sponge/Spigot/Paper/Forge/Fabric-Server. Read the installation instructions to get started!
Special thanks to JetBrains for giving out an OpenSource-Licence for BlueMap development!