Moldy, damp walls in basement or crawlspace!
Updated: Sep 20, 2019
Unfortunately fixing this is not easy. The walls need to be cleaned of grime and efflorescence (the white build up of salts leaching from the concrete) then bleached, then rinsed. Wire brushing is needed to get off any remaining deposits. Then cracks need to be filled and at least two coats of Drylok need to be applied.
Typical scenario when downspout above is discharging directly to the foundation.