This is achievement/objective number 45. You have to visit the page above. Remember though, you need to be logged into Howrse for it to work.
However, you can only ever visit it once - when you are completing the achievement. If you visit it before you have unlocked this particular achievement, or try to visit it again afterwards it will disappear and say the page doesn't exist!
So we've included a picture of it in this post in case you want to see it again. You can click on the picture to enlarge it.
Best of luck with the other new achievements/objectives. Let us know if you have any questions about any of them.