That is actually the way that Nosferatu get up to the penthouse :)!

I'm surprised that nobody has mentioned this yet: you should save the game every two hours, terminate the game, then restart it.

This is the only way to avoid a memory leak bug.

Unfortunately its a bug within the engine and its unfixable because of that. And because its an old game and 32 bit, having more memory also doesnt help; the game cannot address more than 4 GB no matter how much memory your computer actually has.

Anyway this problem is the root cause for many random problems.

I should also mention that his bug still appears even if you merely run the game two hours in the background.