The phrase "monumental effort" means a significant, extraordinary, or extraordinary amount of work or energy put into achieving or completing a task or goal. Full definition
Putting one foot in front of the other took monumental effort. (mindbodygreen.com)
It's taken monumental effort, but your book is finally written and edited. (melaniesaxtononline.com)
I also appreciated Ken Shigley's informative comment on how monumental efforts by bar association employees and volunteers are often stymied by outside forces. (lawyerist.com)