The key to leveling a park bench on a slope is creating a stable, flat base rather than cutting the bench legs shorter. First, measure the slope by laying a straight board where the bench will sit and lifting the downhill end until it is level. Measure the gap underneath so you know how much soil or gravel needs to be removed or built up.
Next, excavate a flat pad into the hillside. Make it several inches wider than the bench footprint and slope the back cut slightly away from the pad so rainwater will not wash soil onto the seating area. Pour in 3–4 inches of crushed gravel or paver base and tamp it down firmly. Check level in both directions before setting the bench in place.
If one leg still floats, slip pressure-treated wood shims, composite shims, or flat stone pavers under the low points. Avoid stacked bricks or loose rocks, which can shift. For a permanent installation, anchor the bench through the feet or use L-brackets into compacted ground, concrete blocks, or poured footings. In cold climates, dig footings below the frost line to prevent frost heave.
On steeper slopes, build a small terrace or timber retaining edge at the downhill side before adding gravel. This stops erosion and keeps the bench from sliding over time. Finally, sit on the bench and check for rocking, drainage, and stability from every direction.