We've had the lawn for, what, almost 4 years now. It is due for an aeration.
Aerating the lawn involves removing plugs of soil (4" deep or so, size bigger than a dime) from various places of the lawn to promote air and water to go to the roots of the remaining grassroots.
Usually lawn-care companies drive by / call / spam about services. They can probably aerate your lawn in no time, but they charge tens, if not hundreds of dollars and use a power aerator.
Instead, Mr. Self-Torture decides to use a manual coring aerator to do the job. Every foot or so, I push the tool into the soil and every push I remove 2 plugs. Repeat ad nauseum, until entire lawn is covered.
Took me an hour to cover all 4 pieces of my lawn in the front, and another half-hour to pick up all the plugs. (normally the plugs would dissolve after heavy rainfall, but they interfere with my reel mower, so I remove them.)