Luncheon of the Boating Party by French artist Pierre-Auguste Renoir. It is 16.5 x 12.75 inches and has 461 pieces. Compared to Renoir's Dance at Le moulin de la Galette, with 754 pieces, this one was easy. Having 303 less pieces and more detail than the other had something to do with that.
It is among the largest paintings Renoir ever made. It took sixteen months to complete. It is one of his largest paintings at 51" x 68" inches, It is considered Renoir's most famous and well-liked painting.
It depicts a real place: Maison Fournaise of Chatou, a floating restaurant moored along the Seine River. It still exits and you can still have lunch there.
For more information, read this interesting article about Luncheon of the Boating Party and how it differs from Dance at Le moulin de la Galette.