First issue to worry about is the flight. Make sure that you keep the money on your body during the flight, there are increasing reports about valuables being stolen by other guests or even flight attendants during long-haul flights from the bags in the overhead lockers.
Another option (if your travel permits) is depositing parts of it in a locker at the train station/airport. Get more when you need it.
Since you are in an apartment, you should be safe leaving items there. If it's a serviced apartment, same things as for hotels noted below apply.
In any hotel, the room safe is the first option. The next option in a good hotel would be to talk to the management and ask them where they would recommend you to "store valuables". They might have another 2-lock safe in the reception area. In a good hotel, you might also be fine with a bag that can be locked, but be aware that something locked will attract thieves, so do not do that in a shady/budget place.
It might be also good if you can find a secret place within your belongings. Soft bags often have a card-board like floor under which items can be hidden. Larger luggage and might have a lining in which items can be placed when cutting open a little corner.
Before I had a credit card, I used to have a leather jacket into which I cut another opening into the lining of the pockets to have access to the space between the lining and the leather. I had another wallet in there with the rest of my money. Like this I had it with me, but it was not visible from the outside.