To cross the huge gap in Plutonia map 2, WELL OF SOULS:

The trick to the pit: There is a bridge across it already,
but it's invisible.
When you first enter the pit area, and you're standing at
its south edge, turn left and you'll see a small window in
the rock wall nearby.
Select your pistol and fire a shot through the window at
the control panel inside.  This causes some "guide posts"
to rise up on the north and south edges of the pit.
Walk a straight line between those posts to cross the
invisible bridge.

PC Plutonia players can click here to access a demo that
shows how/where to cross that bridge.

Hope this helps. :)                                      

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