Lego Duplo Ariel's Undersea Castle by LEGO SYSTEMS Sold out $41.99 1 2 3 4 5 6 7 8 9 10+ Quantity Quantity Status: Sold out Go down under the sea for adventure and fun with The Little Mermaid in this LEGO DUPLO set, ideal for young builders. Ariel and her friend Flounder are spending the day at their underwater playground – and they want you to come too. For ages 2+