Stayed here for 6 nights with wife and 2 boys (aged 9 and 10) to attend a local festival and use a base for day trips.
Staff are very pleasant and efficient. We arrived slightly early but our room was already prepared. We had a mini-apartment on two floors which gave us plenty of space. The boys had a sofa bed each, while upstairs we had our room and the shower room/toilet.
There was loads to eat for breakfast, with the juice, breads, meats and cheeses constantly replenished and kept fresh. A slightly later breakfast than 10 am would have been nicer as sometimes a lie-in would be appreciated.
The hotel reception and (small) bar are only staffed 'til 10 pm, but they let us stay later for a drink and leave a note of what we had!
Only slight downsides would be lack of tea- and coffee-making facilities in the rooms and the lack of lifts if you're on the upper floors. It wasn't a problem to us but could make it difficult for the less fit.
Will definitely consider staying here again if in Mülheim-an-der-Ruhr.
