  We discuss the main factors affecting the design of accelerators aiming to
investigate physics at the GUT scale. The most important constraints turn out
to be the energy used and the time taken to accumulate sufficient luminosity.
We propose a photon collider design, where the photons are generated by
undulator radiation from high energy muon beams. This reduces the energy
requirements by a factor of more than $10^7$ compared to a pp collider. Much of
the reduction in energy use is achieved by using a periodic magnetic field, and
by splitting the muon wavefunctions spatially to reduce the photon beam
divergence; these prevent a cascade of secondary reactions at the collision
points. The proposed collider would be powered by (part of) a Dyson swarm
constructed around the Sun, and efficient use of energy will be important to
reduce the time needed to reach the desired number of collisions. We also
discuss why a neutrino collider would be much less efficient.
