If you don't have it already, you need an X11 server. on Mac OS X/OSX/macOS Sierra: you need to download and install XQuartz.

After that, go to the Sourceforge website, and download the 2.6.0 version of cp2k cp2k-2.6.0.tar.bz2.

Using the Mac terminal, go to the directory where cp2k has been downloaded (if it has been downloaded in the Downloads directory type cd ~/Downloads in the Mac terminal). To unpack the archive files using the command given below

tar -xvf cp2k-2.6.0.tar.bz2

An example CP2K ARCH file for a serial build of CP2K on Mac is as follows:

# With GCC 4.9 or later, for gcc and gfortran
# libxc is installed in LIBXC_INCLUDE_DIR / LIBXC_LIB_DIR
# libint is installed in LIBINT_LIB_DIR
CC       = gcc
CPP      =
FC       = gfortran
LD       = gfortran
AR       = ar -r
RANLIB   = ranlib
DFLAGS   = -D__NO_STATM_ACCESS -D__ACCELERATE
FCFLAGS  = -I $(LIBXC_INCLUDE_DIR) -O2 -ffast-math -funroll-loops \
           -ftree-vectorize -ffree-form $(DFLAGS)
LDFLAGS  = $(FCFLAGS)
LIBS     = -framework Accelerate

Remove the -DLIBXC -DLIBINT flag if you compile CP2K. Save it as Darwin-IntelMacintosh-gfortran.sopt in the cp2k-x.x.x/arch directory alongside the other ARCH files.
Launch the Terminal and change the working directory to cp2k-x.x.x/makefiles. Type make command as follows:

make ARCH=Darwin-IntelMacintosh-gfortran VERSION=sopt

It may take quite a while until a compilation is completed. If you have a multi-core machine you may use e.g. make -j 4 to compile in parallel with 4 tasks.
If you find cp2k.sopt in cp2k-x.x.x/exe directory, then compilation is successfully done.