I tell clients to go outside and walk when they are suffering from anxiety or depression.  The exercise from the walking is a great mood booster.  But even just sitting outside will improve your mental health.  Check out a near by park or just the backyard.  Ten minutes outside will increase your self-esteem.  In twenty minutes you will feel your mood begin to rise.  Being in nature for 30 minutes increases happiness and decreases symptoms of depression.  Having negative thoughts?  Go for a full 90 minute outdoor session.  This length of time changes your blood flow to the subgenual prefrontal cortex, this is the area of the brain involved in negative thoughts.  So 90 minutes sitting enjoying a sunset, walking, or gardening will result in a reduction of negative thoughts.  Give it a try.  What have you got to lose?