ハーグからケルンまでの移動

オランダとドイツの鉄道の違い

それは、前者には関所（改札）があること。後者にはこれがありません。誰もが列車にアクセスできることです。

Den Haag Centraal ab 06:23 5 IC 11721
Utrecht Centraal an 07:00 12
Utrecht Centraal ab 07:06 15 ICE 121
Köln Hbf an 09:12 6
とかですよね。DBでもNSでも同じ価格で買え、Sparangeboteで29,90 EUR。

DBも今や紙に印刷するのは時代遅れで、アプリを使うのが一般的です。これでDBラウンジも入れるし。

NSの場合は関所を通るのに紙も画面（アプリ）もQRコードが必要です。以下をご覧あれ。
Travelling with your e-ticket or mobile ticket

When travelling with an e-ticket or mobile ticket, you can open the gate using the square barcode on the e-ticket or mobile ticket. Not all gates can be opened with an e-ticket or mobile ticket, only those gates with a barcode reader. These are recognisable by the image with ‘scan ticket’ on the right-hand door of the gate, and by the illuminated area on the right-hand side of the gate.
Steps: how to open a gate

Step 1: Go to a gate displaying the 'scan ticket' symbol.
Step 2: Hold the barcode against the illuminated area to your right.
Step 3: The gate opens allowing you to enter or leave the station.

便利なのはやはりこれ。
Mobile phone tickets

Do you make the occasional journey by train, and buy a ticket from the ticket machine or the service desk? You could be doing this faster and cheaper! Simply arrange everything online: order tickets using the NS-app or on ns.nl, pay and load the ticket onto your mobile phone. You don't need to print anything.

関所通過に読み取りが必須なのです。