Underground

1. Music

1.1. Rap/Hiphop

1.1.1. Underground Rap

1.1.1.1. Non commercial

1.1.1.1.1. No Big cashgrab behind the Rapper

1.1.1.2. Indepent Rappers

1.1.1.2.1. The Notorious Big

1.1.1.2.2. 2Pac

1.1.1.2.3. Wutang Clan

1.1.1.2.4. Jay-Z

1.1.1.2.5. Mobb Deep

1.1.2. Conscious Rap

1.1.2.1. Political hip hop

1.1.2.2. A way to comment on politics and other social problem via Rap

1.1.2.2.1. Fuck tha polica by N.W.A

1.1.2.2.2. Stop the Violence

2. Transport

2.1. Metrosystems

2.1.1. London underground

2.1.1.1. Big stations

2.1.1.1.1. Important for society

2.1.1.2. Lot of history

2.1.2. New York City Subway

2.2. Tunnels

2.2.1. Euro Tunnels

2.2.1.1. France to England

2.2.1.1.1. High-Speed Rail

2.2.2. Gotthard base tunnel

2.2.2.1. Switzerland

2.2.2.1.1. Longest Railway tunnel