Yes, Jains can go into a basement or underground space.

The Jain rule about “underground food” usually refers to roots and tubers like onion, garlic, potato, etc., because pulling them out harms many tiny living beings and the plant is destroyed. It does not mean that a Jain cannot go underground, use a basement, or live in a lower floor.

So:

• Going underground: allowed
• Eating underground/root vegetables: generally not allowed in Jain dietary practice
• Reason: ahimsa, to avoid harm to living beings

If a basement is clean and not causing harm, there is no Jain prohibition on entering it.