You can find some information here on how to reach Sinaia.
If you are travelling to Romania by air, then you will be entering our country through the Otopeni airport. There is a shuttle pickup area just outside the airport that can take you to Sinaia.
To reach it, after coming out of the baggage claim area, go left towards the supermarket Express and take the escalator to the lower level. Go out through the sliding doors and go across the entire parking lot and you should reach the shuttle area.
Be prepare to have local currency in cash. A one-way trip to Sinaia costs around 60-75 RON. There are many shuttles during the day, so you shouldn't have to wait more than an hour for one no matter the time of your arrival.
If you are travelling by train, then your endpoint will be North Railway Station (Gara de Nord). In this case, the easiest would be to simply buy a train ticket to Sinaia. Keep in mind that the Sinaia train station is a bit far from Hotel International.
You can walk, but if you have heavy luggage it might be easier to grab a cab.
If you are coming with your personal car then you can use any map application to guide you to the address of the hotel shown at the bottom of the Overview page.