Store painting.

The senior member of staff at the desk, who seems to be aged about 19, politely informs you that the hotel doesn't have safety deposit boxes that big but that she can arrange for a porter to carry the painting to your room if you're finding it too heavy.

You can:

Take the sarcastic little witch at her word and insist on the porter while you hit the bar.

Take the painting to your room yourself, making a mental note to write something disparaging on the hotel's "Let Us Know What You Think (TM)" report card.