How to implement and hide admin zone on the website without login/registration system?

I'm new to web development, and I'm currently making a presentation website(home, services, news, vacancies) for a small company. I'm using Node.js,Express and MongoDB.

The client wants to manage certain content on the website, therefore there needs to be a dashboard, where only admins could login/register. But website design does not provide any login/registration system for users.

The question is, where do I put a dashboard and how should I hide it from ordinary users? Should I just use url, like mysite.com/admin, which should be typed by the admin, whenever he wants to get to the admin login/dashboard zone(it seems quite unsafe, since everybody on the internet could type that and get to the login form)? Or maybe I should make a separate desktop app for managing website content?

How should I approach this problem, what are the best practices?

Thanks!