Creating a standard D&D encounter is pretty easy. You just need some sort of battle map, and a few monsters, maybe a treasure. You can create a whole mega-dungeon by making a large dungeon map, and filling every room with monsters and/or treasures, and it will keep a group occupied for a long time. Making *memorable* encounters is a lot harder. It requires the same ingredients as a standard encounter, plus some original idea.

It turns out that if you are looking for such ideas in the adventure material available for purchase in books or online, those ideas are pretty thin on the ground, and much diluted in a lot of filler material. You can read one of WotC's big published adventures with 250 pages, and end up with no more than half a dozen of original encounter ideas. What I would really like to see would be a collection of just those ideas, without all the filler material around it. "The heroes have to fight saboteurs on a steamship, while undoing their damage in time before the whole boat blows up" is a great idea. But in the adventure I took that idea from, this idea is described over 5 pages of a 45-page document. That is a lot of reading to do, just for finding some cool ideas.

• Go somewhere cool
• Talk to someone interesting
• Learn something new
• Fight something
• and get a reward

With that list you cover both the "roleplaying" and the "game" aspects of Dungeons & Dragons. And typically, the memorable encounter ideas cover all or most of that list. The steamboat is a cool place, the players will talk to interesting people and learn something new, that a sabotage is planned or ongoing. Then they will fight the saboteurs, and get a reward if they saved the boat. And for the ideas in published adventures, the list can help you to identify what is missing if an encounter doesn't seem to be that great. Maybe it's just all fight and loot, but doesn't drive the story forward. Maybe it's all talk, but boring, wasting an hour haggling over the price of armor with the village blacksmith.