German has definitely a number of grammatical ironies. One of them has to do with the verb sich erinnern ("to remember").
By the time you finish saying that you remember something, you probably have forgotten what you wanted to say...
Don't worry, we will cover the usage of this verb step by step, so you don't have to panic every time you need to use it.
Step 1: This verb is reflexive
Ich erinnere. → Ich erinnere mich.
Step 2: You need a preposition to express what you remember (your object)
Ich erinnere mich die Reise. → Ich erinnere mich an die Reise.
Step 3: After "an", you need accusative
Ich erinnere mich an der Urlaub. → Ich erinnere mich an den Urlaub.