Hotel Schlussel or Hotel Beau Séjour in Lucerne?

Both are nice hotels. I believe Beau Séjour is undergoing some renovations over the winter, so not sure what will be changing…generally I think the rooms are bigger and more “design oriented” than Schlüssel. The Schlüssel is furnished in a more classic style (but has been renovated, so bathrooms etc are modern). If summer heat concerns you, I think Beau Séjour has portable ac units in the rooms, while Schlüssel does not have ac due to the historic building structure (fans available).
The other main factor is location and it depends which appeals to you more - Beau Séjour is on the edge of town (15-20 min walk to old town and train station, there is a frequent bus if you don’t want to walk), but is right on the lake with great views. Schlüssel is in a cute square next to a picturesque church, tons of restaurants nearby and easy 5-10 minute walk to old town, chapel bridge, train station etc. So do you want the old town experience or lakeside relaxation?

We stayed at Beau Sejour two months ago. We chose one of the historic double rooms without a lake view. The room was large, immaculately clean, very comfortable bed, large closet with shelves & hangers that give plenty of storage. The hotel provides electrical adapters, and there are multiple outlets. Bathroom.is good sized with a hair dryer and toiletries. The rooms have portable air conditioners which are very efficient. Multiple people told us that A/C was not necessary in Lucerne, but the temperatures were in the mid to high 80s, so we were thankful to have it. There is a lift, so no need to carry luggage up the stairs. Upon arrival, there was a large bottle of water in the room, and it is refreshed every day. The hotel has a bar, and they are happy to refill water bottles with either still or sparkling. The staff at both the front desk and at breakfast was warm, welcoming and accommodating. Breakfast options were plentiful, fresh and included a hot egg dish upon request. There is a beautiful terrace with a view of the lake where you can enjoy your meal. It is about a 15 minute walk along the lake to the old town. A bus passes in front of the hotel, and they provide you with a complimentary Visitor Card Lucerne which covers all your transportation in zone 10. We loved the fact that the hotel was quiet and a bit removed from the hustle and bustle of the tourist area. We enjoyed everything about our stay and can recommend it to fellow travelers.

Keep your eyes out for a big parade in the old town. When I was there last year, it was on June 15th, a Wednesday, around 6:30pm. I’m not sure what it was for. Lots of people in old military uniforms, horses, marching band, the Swiss Guard. I’ll be there around the same time next year and I’ll be looking for it.