Last night I watched 'Troublemakers: The Story of Land Art'. It's a fairly standard documentary in terms of format and full of stereotypical 'arty types' talking in arty cliches, but for me the subject is absolutely fascinating - people constructing huge, grandiose modern monuments with little hope of financial reward, or, to be more accurate, financial riches, as while the artists didn't seem to have much hope of becoming rich themselves, the works weren't cheap to say the least. It's hard to express what I find appealing about it - there's a kind of purity to the art and the motivation, but it's mainly the huge scale of ambition and imagination I love and the links to what our ancestors did with the landscape. Some of the artworks are still in progress over 4 decades later.
Spiral Jetty by Robert Smithson
Double Negative by Micheal Heizer
The Lightning Field by Walter De Maria
Roden Crater by James Terrell (started in 1979, still being finished)
Complex 1 (part of 'City' by Michael Heizer, started in 1972, 2 x 0.4km in size, still unfinished)
Love this stuff. Definitely an ambition of mine to visit most of these some day.