The source code for Athena can be downloaded as a gzipped tar file from this site. To install and run the code requires only a C compiler. After downloading the tar file, uncompress and untar it:

% gunzip athena4.0.tar.gz
% tar xf athena4.0.tar

The following directory structure should be created:

       /apps           problem and input files used in previous applications
       /doc            selected additional documentation
       /src            source code, and include files
           /fftsrc          FFT interface
           /gravity         self-gravity 
           /integrators     unsplit integrators
           /microphysics    resistivity, thermal conduction, viscosity, etc.
           /prob            problem files (/src/problem.c is a symbolic link to one file in this dir)
           /reconstruction  spatial reconstruction algorithms
           /rsolvers        Riemann solvers
       /tst            various input files for tests
       /vis            visualization tools and scripts
           /idl        IDL ( scripts
           /matlab     MatLab .m files   
           /sm         Super Mongo scripts
           /vtk        code to join VTK legacy files

In addition to those above, another directory will be created by the Makefile when Athena is compiled for the first time, using make all.

       /bin           contains executable, created by Makefile

(Trying to compile the code with make compile before make all will result in an error since the bin directory will not yet exist.)