Spherical underground Mars colony by Michel Lamontagne

One of the weak spots for any domed human colony on Mars would be the enormous pressure difference needed between the higher interior pressure suitable for humans (~ 1 bar) and the near-vacuum exterior pressure of the Martian atmosphere (0.004-0.011 bar). The dome for such a structure should have heavy anchoring deep underground. But there is a much simpler solution - a spherical hermetic structure mostly underground where only the tip of the sphere (visible as a dome) is located above the ground level. Sphere is the strongest geometric shape for containing internal pressure and the structure can be kept in place by the mass put inside the sphere.

Canadian design engineer Michel Lamontagne has created two concept drawings for such a colony where there is only a domed park above the ground level and all the rest of the colony is located below the ground level with a vertical central opening for natural lighting:

The geodesic surface dome is subdivided into small panes for easier replacement and safety: