Complex sentence: They build Velu a hut above 30 feet with dug land beneath it, but Velu often gets down and goes to the riverside during the night to meet Malar when the guards are asleep.
Split into simpler sentences: They build Velu, a hut above thirty feet with dug land beneath it. But Velu often gets down and goes to river side during the night to meet Malar when the guards are asleep.