Gladys is visiting
>! [Mohenjo-daro](https://en.wikipedia.org/wiki/Mohenjo-daro)

Solution
>! [![][1]][1]

Step-by-step
>! A basic deduction of Yin-yang is that any two cells of same colour on the border must be connected through the border. Since at least one of R4C9, R5C9 and one of R8C6, R8C7 must be black while one of R6C9, R7C9 must be white, we know that the black region must cover clockwise the border from R8C6 to R6C9  
>! [![][2]][2]  
>!  
>! Next, we can colour some cells just based on the connectivity and 2x2 rules  
>! [![enter image description here][3]][3]  
>!  
>! Another basic deduction of Yin-yang is that in any 2x2 region the two colours cannot "cross" each other. This gives us R3C4 and R6C7  
>! [![][4]][4]  
>!  
>! And the rest is filled up with just those basic deductions  
>! [![][5]][5]


  [1]: https://i.sstatic.net/jtg0T43F.png
  [2]: https://i.sstatic.net/TmaIKOJj.png
  [3]: https://i.sstatic.net/ZzYhOymS.png
  [4]: https://i.sstatic.net/26HwnezM.png
  [5]: https://i.sstatic.net/VCD3pUgt.png