Inconspicuous entrance - Don't bother lookingm there is absolutely no chance you'll find it.
Dubious passage - Its probably a dead sheep you're crawling through, but you can't be certain.
Short technical section - Opportunity to hang upside down by the goolies.
Pleasant streamway - "The lifejackets are under the seat and used thus..."
Low airspace - Yes, if you try, then you CAN breath the foam on the surface.
Letterbox - Practice section for entering bank vault.
Exposed climb - Can't be done irrespective of whether you're clothed or unclothed.
Airy stance - Opportunity to fill wellies from within oversuit.
Well decorated - You deserve a medal for getting thus far.
Awkward manoeuvre - Impossible if you don't work in a circus.
Flat out - Throttle pushed fully to the floor, but you still don't go anywhere.
Mendip cave - All of the above with the addition of copious mud.
Escape route - M5 followed by M6.