The nearest train stations to Schlossplatz 1 are Alexanderplatz and Spittelmarkt. Both of them are about a 10 minute walk away from Schlossplatz 1.
Schlossplatz 1 is situated right in the center of the city. It can be reached easily from both airports either by regional trains (going to Alexanderplatz) or by taxi.
Please note that not all German taxi operators accept credit card payments, so please check with the driver before starting your journey.