Black Castle
After exiting the crack, Mira's group started wandering around the desert again. Since following any sort of direction is impossible and there are no landmarks for them to understand where they are, they are forced to just wander around endlessly until they find something.
They don't really have anything that can help them map out the area so the best thing they can do is just rely on Mira's sense of direction.
What they are looking for is any change in scenery or a change in temperature, whether it be hotter or cooler.
Just like how they found that lotus flower, they scoured the desert until something of interest popped up.
***
Just like the rest of their time in the Secret Realm, they haven't encountered a single person. There were over 100 that entered the Secret Realm, but so far they haven't met a single one. Mira was a bit suspicious of this because she felt like they should've encountered at least one, but unfortunately, there is nothing she can do about it.