If what you posted is exactly what you have in your cshtml, you don't have any closing tags on these elements. You have opening tags, but no closing tags.
<asp:ListBox id="activites" name="activities" runat="server" selectionmode="Multiple" row="1" set="" autopostback="true">
<asp:ListItem>Run</asp:ListItem>
<asp:ListItem>Walk</asp:ListItem>
<asp:ListItem>Hike</asp:ListItem>
</asp:ListBox>