.wrapper {
	display: inline-block;
	position: relative;
}

.overlay {
	position: absolute;
	top: 43%;
	left: 0;
	width: 100%;
	font-size: x-large;
	color: light-grey;
	text-align: center;
	font-family: "Lato","Helvetica Neue",Helvetica,Arial,sans-serif;
}

.city{
	width: 100%;
	height: 100%;
}
<!--HTML-->
<div class="row">
	<div  class="col-md-12">
		<div class="wrapper">
			<img src="img/bg.jpg" class="city">	</img>
			<div class="overlay">
				<h2> Owesome title</h2>
				<button class="btn btn-spec"> Find out more </button>
			</div>
		</div>
	</div>
</div>