Build your mountain using touch/mouse:
• Tap/click and drag red points to move them
• Long-press/right-click to add a new point
• Or use the "+" button to add a new point (tap where you want to place it)

The puzzle is: can the two hikers meet, under the following conditions?
Hiker A starts at the left blue point, hiker B starts at the right blue point, and the altitudes of A and B must always coincide (thus they have to walk in lockstep).

Here we draw all pairs (xA, xB) corresponding to two points at the same altitude.
Thus the puzzle reduces to: is there a path from the bottom left corner of this figure to the diagonal line?