Complex sentence: While there he began planning the design and construction of a suitable mausoleum and funerary garden in Agra for his wife, a task that would take more than 22 years to complete, the Taj Mahal.
Split into simpler sentences: While there he began planning the design and construction of a suitable mausoleum and funerary garden in Agra for his wife. It was a task that would take more than 22 years to complete: the Taj Mahal.