Your city means your present place (must have lived at least an year), your hometown, any place you lived for significant period of time, say 2 years or so.
Landmark means a place in your city or surrounding region which the same is known for.
Inspired by the fact that although I lived in London quite a while, I only went to visit the Tower of London and Buckingham Palace years later, when I had an unexpected free morning during a business trip to that city.
Driving by or near does not count.
In DC, I don’t think I’ve ever inside the Supreme Court, or Congress. I’ve been to the Whitehouse and Washington Monument, but I was a little kid. I’m not sure if I’ve been to all the Smithsonian buildings either, there’s probably one or two tucked away that I’ve missed.
Chicago: Haven’t gone up in the Sears Tower, haven’t gone inside Wrigley Field, Comiskey Park (RIP), US Cellular Field, the United Center, or Soldier Field.
Well, Rochester doesn’t really have a lot of landmark destinations. I’ve been to the Eastman House, the Strong Museum, and the Seneca Park Zoo. I haven’t been to Susan B. Anthony’s House, Charlotte-Genesee Lighthouse, or the Stone-Tolan House yet.
Of course there’s also the waterfalls but contrary to the OP I would think that driving by them/it would count in this case (as long as you’re not the driver and have to keep your eyes on the road), and it would be more difficult to not drive by them.
I have lived on Grand Cayman more than ten years but still have never been to a couple of the tourist traps or historic sites.
Of the landmark locations, I’ve missed out on:
Mission House historic site
East End Lighthouse
Bodden Town Pirate’s Caves
Mastic Trail
Elmslie Memorial historic church
Slave wall
I’m in Atlanta. I have not:
Been to the new World of Coke (been to the old one)
Been to the High Museum of Art
Been to the Atlanta Symphony Orchestra
Been to the Margaret Mitchell house
Been to the Oakland Cemetary.
I’m sure there are others I’m missing.
I’ve never seen the little rock that Little Rock, Arkansas was named after. I lived in Dallas for years but never visited the site of JFK’s assassination.
Geez… same here.. and I feel shame. Never been up the steps of the Lincoln Memorial, never been to the Jefferson memorial, or the Wall, or the Korean memorial. Damn it’s a long list. There are monuments for the Japanese internments, the Men of the Titanic who sacrificed themselves for women and children, Einstein - Man of the Century, etc etc. Never been to Fort McNair which is the 2nd oldest fort in the US. Never been up the Washington monument, or the Cathedral. Now I feel like a slacker.
However, I do know just about every shortcut around the city including the beltway, the Maryland burbs, Northern Virginia burbs, Capitol Hill, Georgetown, Tyson’s, 50, 66, 295, 395, 95… and every golf course within 50 miles. 
Also Atlanta. Never been to the Coke museum because why in God’s name would you?
I don’t live in London any more but I did for four years and have worked here for 15.
The list of sights I’ve never been to is endless.
St Paul’s Cathedral
Tower of London
Buckingham Palace
Madam Tussauds
London Dungeon
You name it, I haven’t been inside.
I lived in the SF Bay Area for years, but never went to Alcatraz.
In Toronto, I haven’t been to Casa Loma or Maple Leaf Gardens.
Can’t think of any place big that I hadn’t been to in the town I grew up in, or the various places around Florida where I lived, including Orlando unless you count the Morse Museum in Winter Park, which I don’t because it’s far from on the top 10 list in the Orlando area.
However, I did live in Ithaca for 2 years and never went to Moosewood Restaurant.
I live in Boston;; never been to the Top of the Pru, taken a Duck Tour, or gone to the new Boston Tea Party ship, but that’s about it. I’ve even gone looking for obscure sites that are mostly forgotten by now.
I grew up near Seattle, but never took the Underground Tour.
I live in the Boston area and I have never done any of those either. I have also never been on the USS Constitution, walked the whole Freedom Trail, visited the Isabella Stuart Gardner museum or the Museum of Fine Arts. I have never been to a Patriots or Bruins game either (I went to my first Celtics game last year because work gave me box tickets).
I’ll see those and raise you:
Ebenezer Baptist Church (Where MLK, Jr preached)
The Carter Center
The Georgia Aquarium (odd, since I have been to aquariums in Chattanooga, TN; Baltimore, MD; and Charleston, SC)
Portland, OR; resident for the past three years. We’ve seen pretty much all of the city, all of the surrounding area, and most of the state including the entire coast with all of its lighthouses. This includes Mt. Hood, Mt. Saint Helens, Crater Lake and the entire John Day area. Also been to the Pendleton Roundup, all over both the northeast and southeast parts of the state.
Prior to here, we were in Alaska for ten years, during which we traveled every available road, including up to the North Slope. My job took me to the remotest parts of the state. We didn’t see it all, but made a sizable dent in it, including: Denali Nat’l Park, Katmai Nat’l Monument, Valley of 10,000 Smokes (in Katmai Nat’l Park), photographed polar bears on Barter Island, walked on glaciers, etc.
This is a pattern that we’ve followed during the 20 years we’ve been together, regardless of where we live, whether in the US, Africa or Europe. I feel very fortunate.
I’ve spent most of my life in the Pittsburgh area and have seen it all.
Spent four yours in Philly, but other than the Franklin Museum I saw nothing. I was in school, plus I never learned the area. I set out to see the Liberty Bell a few times, but one-way streets and a short fuse got in the way each time.
I forgot one: I haven’t visited the Hockey Hall of Fame, either.