The Staircase in the Woods by Chuck Wendig

 

The Staircase in the Woods by Chuck Wendig - 400 pages

Five high school friends are bonded by an oath to protect one another no matter what.

Then, on a camping trip in the middle of the forest, they find something a mysterious staircase to nowhere.

One friend walks up—and never comes back down. Then the staircase disappears.

Twenty years later, the staircase has reappeared. Now the group returns to find the lost boy—and what lies beyond the staircase in the woods. . . .

This was a little of a slow burn in the beginning, but it soon became unputdownable.   A creative idea and a bit creepy.  A great read for fans of horror.