Inspired by the Yankee Republic.

Its a tree in the kids backyard in an old house their family moved to.  It is not young but not particularly old.  Big enough, just barely, to have a kid-sized hole in the trunk.  When the kids crawl in, they discover it is much larger on the inside.  They are on the top landing of a staircase that stretches down down down into a distant blue haze.  There are regular landings as far down as they can see.

They go down one level and see a hole to exit.  They crawl out and find themselves in the recent past.  But not exactly the past as we think of it.  The past of our present turns out to be a pale reflection of the real past.  Each time period has its own past appropriate to it that only echoes but is not the real past.  The further back you go, the more different the reality.

For instance, their first exit takes them to colonial times, which are much like ours, but with haunts and ghosties and more swashbuckle.  In the real past, George Washington had a scar down his face and was blood brothers with the Bear of the Woods.  He won the Revolution personally dueling Cornwallis in the final assault on Yorktown.

The real dinosaurs had deadly colors our eyes can’t see and every creature sang.  The T-Rex sprinted with a high shrieky bagpipe skirl while its prey rhythmically boomed.

The kids explore and have adventures at the different levels.  Each level down the tree is taller.  In the far past, the tree is too tall to be seen.  Its massive trunk, bigger than cliffs, disappears into the clouds.

One days the kids ask themselves why the tree is normal size in their own time.