"Dw i wedi mynd i'r parc heddiw."
Translation:I have gone to the park today.
Oh, yes, definitely! One of the course contributors thought that this sentence would be OK. It's clearly not, but there you go.
"Dwi wedi bod i'r parc (heddiw)" - I have been to the park (today) (using bod) "Dwi wedi mynd i'r parc" - I have gone to the park (using mynd)
This was a bit of an experiment in the first course. From classroom experience I thought it would be useful to teach a very simple way of talking about past events while avoiding all the complications of Welsh such as mutations and an infinite number of ways of saying 'yes' and 'no'.
This wasn't popular with Duolingo users who, mostly, wanted to learn completely correct forms rather than an easy workaround and so to avoid the deluge of criticism it has been much reduced in the revised course.