Short answer for household Jains: Yes, using underground things like metro, subway tunnels, basement offices or basement parking is generally allowed.

A bit more detail:

1. What Jain dharma actually forbids here

- The main issue is creating himsā (violence) by: - digging soil (harming earth-bodied beings, prithvī-kāy jiv), - cutting roots, etc. - During construction of tunnels, basements, etc., a lot of digging and harm has already happened. That is where the main pap (bad karma) is.

1. Using vs. building

- Building / ordering construction of new underground structures involves direct himsā and should be avoided as far as possible, especially for things that are just for comfort or luxury. - Using something that is already built (public metro, existing basement parking) is considered a worldly necessity (vyavahār) for most śrāvaks (lay Jains). The major harm was already done in the past; your use now doesn’t add significant new himsā.

1. Difference from eating root vegetables

- Roots (potato, onion, garlic, etc.) are avoided because: - they contain countless tiny lives, - you destroy those lives freshly each time you eat. - Travelling or parking underground does not involve that kind of direct, fresh killing every time you go there. So the rule is not parallel to root-vegetable prohibition.

1. Practical guideline for a lay Jain

- It is acceptable to: - travel by metro or underground train, - park in an underground parking, - work or live in an existing basement. - Try to: - avoid commissioning unnecessary new deep basements or heavy excavation for luxury, - choose less-violent options when they are reasonably available.

1. Monks vs householders

- Munis and sādhvīs follow much stricter mahāvrat; they avoid all avoidable himsā as far as humanly possible. - Householders follow anuvrat: reduced vows, adjusted to practical life. Using existing underground facilities falls under this practical adjustment.

So, for you as a lay Jain: yes, you may use metro, subway, and basement parking, while keeping in mind the broader spirit of minimizing new violence wherever you can.