This is not a complete solution, but more pointing you in the right direction:

Under Settings, Select the DocumentType you´d like to have a gallery, Add a property called Images of the DataType Media Picker and tick the option Pick multiple items.

In your Template, referencde the following CSS and JavaScript:

<link href="https://cdnjs.cloudflare.com/ajax/libs/lightbox2/2.8.2/css/lightbox.css" rel="stylesheet">
<script src="https://code.jquery.com/jquery-2.2.1.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lightbox2/2.8.2/js/lightbox.js"></script>

(Remember that CSS should be in your head and your scripts sholud be in the bottom of your body.)

Then add the following code to render the gallery:

@foreach (var image in CurrentPage.Images.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries))
{
    var media  = Umbraco.Media(image);
    var imgSrc = media.umbracoFile;

    <a href="@media.umbracoFile" data-lightbox="roadtrip" data-title="My caption">
        <img src="@imgSrc"/>
    </a>
}

(Then if you´d like you´d want to refactor this to make is look prettier, i wrote this very quickly to give you an idea.)