Nginx can handle the rewrite parameter differently, depending on the destination syntax. 

Here are some examples how to define redirects and URL rewrites in nginx.

server {
    server_name www.example.com;
    root /var/www/www.example.com;

    location / {
        rewrite ^/$ http://websrv1.example.com/mypage redirect;
    }
}

This will result in forwarding the browser to http://websrv1.example.com/mypage. The redirect address will be shown in the address bar.

Let's try this without a redirect or permanent option but with break or last:

server {
    server_name www.example.com;
    root /var/www/www.example.com;

    location / {
        rewrite ^/$ http://websrv1.example.com/mypage last;
    }
}

Although the rewrite option is now set to last, the browser will still follow the URL and changes the URL in the address bar.
The reason for this is the http:// which is interpreted as external redirect.

So if you want to keep your domain and simply want to rewrite the URL (like in Apache with mod_rewrite), you must use a relative path:

server {
    server_name www.example.com;
    root /var/www/www.example.com;

    location / {
        rewrite ^/$ /mypage last;
    }
}

This will load the website for www.example.com from the subfolder /mypage within the document root (/var/www/www.example.com). 

But what if the destination website is loaded from somewhere else, for example from a Tomcat server in the background?
The following configuration covers this:

upstream tomcat {
    server 127.0.0.1:8080;
}

server {
    server_name www.example.com;
    root /var/www/www.example.com;

    location / {
        include proxy-settings.conf;
        proxy_pass http://tomcat;
        rewrite ^/$ /mypage last;
    }
}

First everything (location /) is passed to tomcat (the defined upstream server). Then the redirect for the root path (/) is happening and is relative to the path.
This results in keeping the browser's address URL at www.example.com but loads the website from 127.0.0.1:8080/mypage.