Hi,
Will most museums and restaurants be open?
Museums and restaurants will be open, no need to worry about that. Due to Easter (many take time off work and schools are on break), some may even extend their opening hours a bit. However, it is a different story for stores. There are 4 public holidays in Easter, in 2026 they are the 2nd, 3rd, 5th and 6th of April. On these days, most stores are closed byt law. Only a limited number of smaller stores remain open. It will not be a problem, unless you really want to go shopping on these days.
Will it be too cold to enjoy the city?
Danish weather is known to be unpredictable. Nobody can tell you what the weather will be like in April yet, and it’s a month that can have vast differences in weather. It will most likely be around 5-10 degrees C, which is the average for that time of year. But there is a (smaller) change/risk for vastly different weather. The extremes range from snow and temperatures below 0 degrees C to sunny and temperatures exceeding 20 degrees C. These extremes are unlikely in April, but it has happened before.
Check the forecast a few days before you travel, and pack layers so you are prepared for a bit of everything.
The Admiral or NH Collection?? Looking for a nice, quiet hotel.
Haven’t stayed at either Admiral or NH Collection, but regarding their locations, I’d probably pick Admiral. Both are by the harbour, which is nice.
Admiral is a bit closer to the main ‘tourist area’ and the historic city centre. Thus a bit more international/touristy, but high-end and significant area. Walking distances probably a bit shorter from here (on average), though the walk to the nearest metro station is a bit longer (but it is served by all metro lines). NH Collection is on Christianshavn, a historic former industry and working class neighborhood that has been gentrified. Thus a bit more 'local', but in a high traffic corner of Christianshavn. Walking distances will be slightly longer (on average), though the walk to the nearest metro station is shorter (but served by fewer metro lines).