Poirot fans who happen to visit Brussels might be interested in the following -
The elegant hotel that features in The Chocolate Box is the Hotel Metropole in Brussels. The ground floor areas (but not all rooms) have retained their impressive early 20th century decor. You can see many photos by going to www.metropolehotel.com or by going to Google images and searching with the words "Metropole Hotel" "Brussels".
The gigantic law courts building where Poirot is shown in flashback in his previous career as a police officer is the Palais de Justice in central Brussels. It was the largest public building in the world at the time it was built, and it's still one of the largest, larger than St Peter's in Rome. It's open to the public and is worth a visit not only for the Poirot connection but also to be amazed by the vast entrances, the huge vaulted spaces and stairways, eclectic style and decorative sculptures. The guidebooks don't do it justice, no pun intended. To see photos use Google images and search with the words "Palais de Justice" Bruxelles or Brussels.