Now, I get why people ask this. Sometimes you just want to check in on someone without making it a whole thing. An old friend, someone you used to be close to, a situation where seeing that you viewed their story would cause more drama than it is worth. That is just a normal human thing to want. 
The tools GorillaBlink mentioned are the main ones people use. StoriesIG and a few others have been around for a while. They are not perfect and they go down sometimes, but for a one off check on a public account they generally work fine.
What I will say though is if you are checking regularly, or if it is someone whose account is private, those tools will not help and the situation probably calls for a different approach entirely depending on what is actually going on.