The Lough Tay, located in the Wicklow Mountains, about 50 km south from Dublin, is also known as the Guinness Lake due to its shape and colours.
The white sandy beach on the northern coast makes the Guinness foam. The brown colour of the water close to the beach (due to the water coming from the streams that rise on peat covered uplands) complete the incredible visual similarity to the famous Irish pint.
You can see the lake from the R759 scenic route, or if you want a better view from the top, take the walking trail towards the Luggala mountain (accessible from the R115 — the best scenic drive in the Wicklow mountains) or the Djouce mountain, one of the most spectacular walks in the Wicklow Mountains, from which you can see the whole Dublin bay and, on a clear sky day, also the Welsh coastline.
The Lough Tay beach was chosen in 2013 as the set for the village of Kattegat in the Vikings tv series.