Build a large underground base that...

Build a large underground base that is perfectly circular, 600 blocks in diameter, with 7 stacked levels. The structure must be fully enclosed and sealed, with no exposure to the outside. Keep the design symmetrical, with a central vertical core connecting all levels. Each level should have a central hub with evenly spaced corridors extending outward in a radial pattern. Ensure all levels are fully connected and easy to navigate. Include a surface entrance centered above the base that connects directly to the core. The entire structure should be complete, seamless, and fully finished, with no missing sections or cut edges.