The Mausoleum
Ye Yan walked down the stairs, going deeper inside the mausoleum. After a few minutes, he reached the end of the stairs but the path continues into a long and narrow passage.
Ye Yan keeps walking with difficulty in the dark corridor because the ground has many bumps and even with the light provided by the firefly in the bottle, he can't see everything around him.
The firefly in the bottle isn't the best option as a light provider but it is one of the cheapest and safest ways to illuminate his path.
If he used a torch, it would illuminate a bigger area but he would need a lighter, and a mausoleum is not the best place to use fire because it could have flammable gases inside.
Ye Yan can't use magic, so cast light isn't an option, and lanterns are sold in few shops in limited quantities, so when he discovered about them, it was already too late because every lantern in the shop was sold out and he didn't have the time to wait for it to restoke.