I’m with you. While the fitness of doing 500km in two days any way you like is incomprehensible for me.
The challenge of doing ‘that’ indoors is zero.
???? It is 500 miles over 8 days. Which makes the indoor challenge unchallenging.
PS - I didn't think doing it in the Southern Hemisphere was challenging either, unless exceedingly hot. Doing it in southern Spain must be pleasant.