The spiraling snail mount was a favorite of the Elizabethans, included in an entertainment staged for Elizabeth I at Elvetham in 1591 in which the snail mount 'resembleth a monster', and was fired upon with cannon (see it there in the lower right corner)
Sir Francis Bacon's garden (c. 1620) had 'in the very middle, a fair mount, with three ascents, and alleys, enough for four to walk abreast; which I would have to be perfect circles...and the whole mount to be thirty foot high'. The snail mount was was a logical response to the desire to view a flat garden from a high overlook, and its wide, spiraling paths a practical way for heavily skirted ladies to ascend on a gentle incline.
The best surviving example is at Lyveden New Bield in Northamptonshire, where twin snail mounts arise from a moated landscape surrounding Thomas Tresham's haunting, never-finished Trinitarian retreat. (Highly, highly recommended for a visit.)
The horticulture students at Cornell University made a smaller construct...I particularly love the idea of a group of people 'walking in' the spiral to the top.
An even earlier model is the medieval turf seat (there's a good historical overview at the Met garden blog), which was sometimes just a shaped area of turf, with or without a seat back, but could also be framed into the seat shape by wattles or boards or masonry.
There's been a resurgence of interest in these 'green sofas' in the last few years....instructions for making a 'sprout couch' can be found at ReadyMade magazine, and there is a commercial kit for making a turf 'chair'. But I prefer simpler, less literal constructs, like this one from the Goresbrook park in Dangenham:
Or these by environmental artist Angela Ciotti from a 1983 installation in Pennsylvania:
And my favorite is the idyllic example painted by Ilya Repin in the waning, dappled days of the Russian elite.
Also note some earthworks previously featured on the blog: Maya Lin's wavefield, and the playhills of Dani Karavan and Parklife London.
Much more could be done with turf on playgrounds, so take this as inspiration!