The best adventure games like Ico are Shadow of the Colossus, The Last Guardian and Brothers: A Tale of Two Sons. Below are 7, each with the reason it is here — and, at the end, what filtering to adventure costs you.
Filtering to adventure means the place and the story are what you want back, not the challenge. It is the right filter when the thing you remember is where you were rather than what you did.
What you get: A world with a reason to wander it, and writing that survives being read rather than skipped.
What made Ico worth playing in the first place is covered on the full list. This page is the adventure part of that answer, and only the adventure part.
The same team's next game — same silence, same world, boss fights instead of puzzles.
Team Ico's direct return to the companion mechanic, with an animal that has a mind of its own.
Two characters on one controller — the companion is a control scheme, not an escort.
Wordless companionship with a stranger, and the same restraint.
Openly Ico-inspired: an island, a boy, environmental puzzles, no dialogue.
A companion who is also the obstacle, in a game about something harder than it looks.
For the sparse, confident puzzle design and the trust it puts in the player.
Mechanical depth. Several of the best adventure games have combat that is deliberately unsatisfying, because they want your attention somewhere else.
Specifically, these are strong answers for Ico that are not adventure games, so they are not on this page:
The full list is on games like Ico — 9 picks, no genre filter.
Shadow of the Colossus. The same team's next game — same silence, same world, boss fights instead of puzzles.
No. Ico released on the PlayStation 2, but a recommendation is only useful if you can play it, so the picks above span platforms and eras. What they share is the genre and the reason.
Anywhere the story and the place matter more than the skill ceiling — point-and-click, walking sims, narrative thrillers and most open worlds. The label alone tells you very little, which is why each pick here says what it actually is.
They split hard. Open-world adventures run to a hundred hours; the narrative ones are often finishable in an evening, and the short ones are usually the better written.
By hand. Each pick was written for the full Ico list first, on what the game actually does, and this page is the part of that list that is adventure — never a genre tag lookup, which is how "best racing games like Super Mario 64" used to be a page on this site.
Or read the adventure guide for where to start in the genre generally.