  Moir\'e magnetism featured by stacking engineered atomic registry and lattice
interactions has recently emerged as an appealing quantum state of matter at
the forefront condensed matter physics research. Nanoscale imaging of moir\'e
magnets is highly desirable and serves as a prerequisite to investigate a broad
range of intriguing physics underlying the interplay between topology,
electronic correlations, and unconventional nanomagnetism. Here we report spin
defect-based wide-field imaging of magnetic domains and spin fluctuations in
twisted double trilayer (tDT) chromium triiodide CrI3. We explicitly show that
intrinsic moir\'e domains of opposite magnetizations appear over arrays of
moir\'e supercells in low-twist-angle tDT CrI3. In contrast, spin fluctuations
measured in tDT CrI3 manifest little spatial variations on the same mesoscopic
length scale due to the dominant driving force of intralayer exchange
interaction. Our results enrich the current understanding of exotic magnetic
phases sustained by moir\'e magnetism and highlight the opportunities provided
by quantum spin sensors in probing microscopic spin related phenomena on
two-dimensional flatland.
