Conversation so far:
is great britain part of the continent of europe
The most common definition of continental Europe excludes continental islands, including Great Britain and Ireland and surrounding islands.
how is great britain connected to europe
Great Britain is physically connected to continental Europe through the undersea Channel Tunnel.
when was the channel tunnel built
The Channel Tunnel began construction in 1988 and opened in 1994.

Question: what is the tunnel's lowest point
Self-contained rewrite: what is the channel tunnel's lowest point