Thunder Hole is located in the one place in the country where mountains actually touch the sea.  It is an amazing testimony to Mother Nature, where, when the tide turns, a thundering impact of the frigid North Atlantic ocean waves force tons of gallons of sea water into a natural stone crevasse.  The sound is thrilling and deafening.  Seagulls calmly ride the precipitating waves while colorful lobster boats saunter by just off the coast.  Located on the rocky Maine coastline in Acadia National Park, it is something that fascinates children and seniors alike.  Savvy visitors wear sneakers, rain ponchos and bring an extra layer of clothes because the weather can change so quickly.  Bring your camera and a favorite book and sit on one of the outlying rocks -- until the tide comes in again!  The show is best approaching high tide.  What time?  Ask a local.