Words to Describe tunnels

How tunnels often is described ("________ tunnels")

• empty
• shallow
• foot
• secure
• smaller
• hidden
• lateral
• longer
• hypersonic
• subcutaneous
• many
• alpine
• diameter
• several
• deep
• parallel
• vertical
• twin
• small
• underwater
• wind
• shaped
• speed
• huge
• main
• pedestrian
• lined
• subterranean
• artificial
• osseous
• tibial
• underground
• subglacial
• low
• short
• deeper
• longest
• green
• track
• unlined
• tiny
• silken
• circular
• endless
• bony
• spiral
• driven
• labyrinthine
• long
• separate
• horizontal
• larger
• narrow
• supersonic
• subaqueous
• plastic
• large
• numerous
• encrypted
• larval
• secret
• vehicular
• concrete
• dark
• extensive
• subsonic
• elaborate
• multiple
• bored