Final answer:
The provided sentence contains an error in punctuation and should be corrected by adding a comma.
Step-by-step explanation:
The sentence provided contains an error in punctuation. The phrase 'although long and hot' is a subordinate clause that should be separated from the main clause with a comma. The correct sentence would be: 'The walk to the waterfall, although long and hot, was well worth it in the end.'
In this case, we are focusing on English grammar and punctuation. It is important to use correct punctuation to ensure clarity and readability in written communication.