The 'cloud thing' is the reason for the walkway.
This is a place near Reykjavik where boiling water seeps up through the ground.
Hydrothermal vents provide all/most of Iceland's electricity and heat.
this is further north, near a big facility for processing the super-heated water.
This is the outflow - still very hot.
The Icelanders have a casual attitude towards obvious dangers; they post a sign and let you figure it out.