Would strongly disagree on
The leaning tower of Pisa. The story that goes with it is great alone, it's a world famous landmark and the design is still unique. You can enjoy the leaning effect of the building from several streets not just from piazza dei miracoli where all the idiots are holding their hands up. Besides, so very amusing that everyone around you are acting like fools. Pisa has more to see than the Torre Pendente alone.
Manneke Pis. Unlike the little mermaid, you don't have to go very far to see it and it's free. It is right there one street aside from the grand market square. Yes the statues tiny, but unless your main aim for Brussels is to see this..
My own picks:
The spike in Dublin. Words fail me to say anything about it. Looks completely meaningless. The financial funding, the long delay and what it is supposed to replace in the first place is more interesting though
The spectacles bridge. Never understood why Nagasaki promotes this as one of it's biggest attractions. The reflection in the water is supposed to make the bridge look like a pair of glasses.
Mount Lofty in Adelaide. Has to be one of the worst vistas I have ever seen from a viewpoint, you do not have the sensation for a second standing on top of a mountain.
I don't think Gdansk is disappointing and there is so much to see in this area, but the only mistake I made during that visit was to spend time at a Prussian fortress ruins a bit out of the city. It was quite literally a ruins, unmaintained bunch of bricks covered in high grass and weed surrounded by dull empty Polish countryside.
The Titanic Experience, Belfast. No genuine artefacts there, just information on displays, cards and pictures and very expensive admission about 15 quid. Also building resembles more of some sort of giant futuristic X-box console to me. Heard the building structure has cost a few million GBP and now they want to demand ROI by day robbing every visitor blind. Tripadvisor has awarded them the travelers choice badge 2017, unbelievable.
Alcatraz. I absolutely don't understand it's popularity. Once you get on the island it is packed with tourists to the brim for something that isn't there, for just a bunch of cell blocks and birds. If I can recall correctly you could only buy pet water bottles for a dollar and tacky souvenirs like a brass prison door key around ten dollars. I had no idea how quickly to leave and the only thing I liked was the big Alcatraz logo. Striking that there are almost no negative experiences with Alcatraz, the most complaints you can find are about.. how soon the tickets are sold out
Scotland has tons of natural beauty. Isle of Skye, Isle of Mull, Cairngorms, Glenn Afric, Ullapool etc etc why anyone would still go visit Loch Ness instead is beyond me. I have seen it several times when I was on the bus and witnessed most tourists get off at this lake.
Speaking of lakes, Bowness on Windermere was pretty dreadful. Not a great lake by any means and the nearby Derwent water lake is much nicer. Bowness is full with tourists, even a few weeks/month after summer season. The traffic is horrible, the local bus is insanely expensive. I have spend 30 quid in total for a few rides. The locals were rude too..
The north cape (Nordkapp) is quite a hassle to get to. It is on a island mageroya which you cannot access without paying toll ), you know, in totally not cheap Norway. (about 15 gbp for a car and then 20 gbp per person to enter! ~heard the entire plateau is overtaken by a hotel chain that needs to make money out of it. Once there you are depending on absolute clear weather for the entire night or else you cannot see what you are after. A glowing orb that stays halfway in the sky then starts rising again..that's all. If you want to experience midnight sun, you could basically do it anywhere in northern scandinavia. Besides it is not even the most northern point in Norway.
From the most northern point of Europe to the most western. Cabo the Roca. The cliffs aren't really that spectacular unless you have never seen cliffs in your entire life and it is next to impossible to get a very good view on them. You cannot wander off far away and there is actually a very tragic story of a Polish family that died when they fell off while making selfies. There is so much to see and do in Lisbon for months, it is not really worth it to go there just to say you have been to the most western point of mainland Europe.
Not precisely a tourist destiantion but a could have been: Hiiumaa island, Estonia. Absolutely nothing special to see there besides a tower, light houses and the same birches over and over. One of the most boring landscapes I have ever seen. Had someone convince me only a few days before my plans to travel Hiiumaa instead of Saaremaa. The latter is a quite popular island in Estonia. They told me that Hiiumaa was wilder and raw whereas Saaremaa was spoilt by tourism. I suppose they meant that sarcastically.