jMC2Obj is a free and open-source application that allows you to convert a Minecraft map into an OBJ model loadable by many popular 3D rendering suites.
jMC2Obj was written in Java and comes with an easy to use graphical interface. It supports both the old region and the new Anvil save file format.
Detailed instructions on how to install and use the jMC2Obj utility on your Mac are available HERE.
jMC2Obj is a cross-platform utility capable of running on any operating system that comes with Java support (e.g. Mac OS X, Windows, Linux).