In Paris, what is the most efficient way to get from arriving on the Chunnel from London to Gare Monparnasse? This will be during the day on a Saturday. If taxi, approximate cost? Reasonable expected time?
No. 4 Metro line will get you there in less than 30 minutes for 1.70 euro. There is a short underground walk to the station from Gare du Nord, and a longer underground passage (partly with moving walkway) to Gare Montparnasse.
Most efficient, dunno, a taxi would be more expensive but faster, but 14 stops on the southbound Métro number 4, direction Mairie de Montrouge - get off at Montparnasse Bienvenue - should do it.
You may find Americans referring to the Chunnel but if you want to speak to British or French people on this side of the water you will get more of a response by calling the train by its name, Eurostar.
Chunnel is is a portmanteau of Ch-annel T-unnel so to arrive on a chunnel you would have to ride on a tunnel. The expression isn't used much anymore here.
Sam and I posting at the same time...
As long as your packing only a carry-on I would choose the metro, I find Paris very easy to get around in using the Metro and is (in my experience) just as fast as a taxi.