Complex sentence: On the east side of the park, adjacent to the boundary with the North Circular Road is what is left of the Japanese water-garden, laid out in 1901 as a home for Leopold de Rothschild's water lilies.
Split into simpler sentences: On the east side of the park, adjacent to the boundary with the North Circular Road is where the Japanese water-garden used to be. It was laid out in 1901 as a home for Leopold de Rothschild's water lilies.