I would say walking around into any direction at the Arena property is not necessarily safe. Unless you would leave valuables at the hotel (as I always do in an unknown city). But there are a number of shops and restaurants within 10 minutes if that is what you like. I is a fairly new area. You could always take a 10-15 minutes tube/train to downtown, the station is next to the hotel.
The Centre East property is in a more safe area, but there's not much going around nearby. It is an area that is a mix of old and new residential buildings and offices. There's more different things to see, harbor, residential areas that allow no cars, side by side to 100-year old streets. But you could also take a tram downtown or even walk to it and take the tram back. I like the hike towards the Y-brewery cafe, but it closes at 8 PM.