When Victor arrives back to Geneva, why is he unable to enter the town> what does he do instead?

From the text:

"It was completely dark when I arrived in the environs of Geneva; the gates of the town were already shut; and I was obliged to pass the night at Secheron, a village at the distance of half a league from the city. The sky was serene;

and, as I was unable to rest, I resolved to visit the spot where my poor William had been murdered. As I could not pass through the town, I was obliged to cross the lake in a boat to arrive at Plainpalais."