Use an iframe. When the user clicks the link, pass the url to be used to your .aspx page. In Page_Load, get this url and load it in to the iframe.
For example, given below has to be in the .aspx page
<iframe id="embeddedContent" runat="server" width="98%" height="1000"></iframe>
Then in your code behind, you could just do
protected void Page_Load(object sender, EventArgs e)
{
embebeddedContent.Attributes["src"] = "some_url";
}