Spirit encounters cannot be responded to. Rather, you receive a description of what has happened. A character can be reduced to 1 health or killed, or if successful can gain gold or an artifact.
Barrow spirits can appear at any ruins, and seem to be the weakest of the various spirits. The character who gets this encounter has a 50-50 chance of either being attacked or gifted with gems worth up to 25,000 gold. This encounter isn't very dangerous unless the character involved has an extremely low challenge rank. (Bobbins)
Spirits are easier than Spirits & Wights.
Character Encounter
Guardian spirits appear at a number of fixed locations, and are more powerful. These locations include: