  Moir\'e superlattices in two-dimensional (2D) van der Waals (vdW)
heterostructures provide 20 an efficient way to engineer electron band
properties. The recent discovery of exotic quantum phases and their interplay
in twisted bilayer graphene (tBLG) has built this moir\'e system one of the
most renowned condensed matter platforms (1-10). So far the studies of tBLG has
been mostly focused on the lowest two flat moir\'e bands at the first magic
angle {\theta}m1 ~ 1.1{\deg}, leaving high-order moir\'e bands and magic angles
largely unexplored. Here we report 25 an observation of multiple well-isolated
flat moir\'e bands in tBLG close to the second magic angle {\theta}m2 ~
0.5{\deg}, which cannot be explained without considering electron-election
interactions. With high magnetic field magneto-transport measurements, we
further reveal a qualitatively new, energetically unbound Hofstadter butterfly
spectrum in which continuously extended quantized Landau level gaps cross all
trivial band-gaps. The 30 connected Hofstadter butterfly strongly evidences the
topologically nontrivial textures of the multiple moir\'e bands. Overall, our
work provides a new perspective for understanding the quantum phases in tBLG
and the fractal Hofstadter spectra of multiple topological bands.
