Final answer:
The Royal Botanical Gardens were built at the north end of the Burlington Heights after the Great Depression, providing jobs and later becoming a key botanical center.
Step-by-step explanation:
The construction that took place after the Great Depression at the north end of the Burlington Heights was the Royal Botanical Gardens. The Royal Botanical Gardens were established in the early 1930s as a project to provide employment during the economic downturn. It has since grown to become a major tourist attraction and a center for botanical science. Although Dundurn Castle is also located on the Burlington Heights, it was built earlier in the 19th century, well before the Great Depression. Dundas Peak and Tiffany Falls are natural landmarks that were not 'built' but rather have existed for thousands of years.
Answer: B. Royal Botanical Gardens